SPECPR Users’ Manual                                                   Page 2.1

CHAPTER 2

PROGRAM STRUCTURE

2.1 Block Diagram of Program Structure Specpr is a menu driven program.

The main menu allows access to the processing parts of specpr. From here the user types a letter or sequence of letters to get to other parts of the program, such as math or display. The main menu looks like:

  __________________________________________________________________________
   v = spdemos : f    1    w = *unasnd*: f    1    d = *unasnd*: f    1
   u = *unasnd*: f    1    y = *unasnd*: f    1    s = starpack: f    1
   lp: spoolfile       obs lat=    .000 deg   channels= 256 wav fl=C  256 h
   file protection: v    53,w     0,d     0,u     0,y     0,s     0 ltype= 0
  --------------------------------------------------------------------------
   MAIN MENU: ********** Program Operations Control *********************

    INFO:     "in" to turn OFF information

    LIST:      l followed by v,w,d,u,or y  to list the contents
                           of the corresponding file
     DISPLAY:   t  to DISPLAY on screen, OVERLAP on screen
     MATH:      m  to do MATH operations
     TRANSFER:  t  to TRANSFER (COPY) files

    PLOT:      p  to PLOT SPECTRA on PLOTTER/printer
     SETUP:     b  to change SETUP PARAMETERS
     FILES:     r  to REASSIGN files and devices
     STARPACK:  s  to create a STARPACK for extinction corrections
     PRINT RST: f  to print summary of the current restart file

    EXIT:      EX  to exit program
  __________________________________________________________________________

Figure 2.1-1 shows the basic user control structure and the commands used by the user to access each section.

2.2 File Structure from the User’s

View The file structure of SPECPR is the most complicated portion of the program. As far as the user is concerned, there are 6 "Devices" each labeled by a single letter (called "file ID letters"). Originally, these IDs referred to a style of processing (e.g. put raw data in the "rawfile" and processed data in the "savefile". Specpr has evolved beyond this simple concept, but the file ID letters are still in place, so the ID letters are now historical. They are:

          v= saVefile (Vfile)
          w= raWfile (Wfile)
          d= workfile (formerly Diskfile at MIT) (Dfile)
          s= Starpack file
          u= Ufile
          y= Yfile

Normally the user assigns, via the file assignment routine (section 5), all of the "devices" to disc files. Sometimes, processed data is stored on magnetic tape and thus needs to be transferred to the disc. Originally, devices u and y were intended to be used only for transfer and display and were not used in any math operation. However, due to increased needs, they have been made full working files (in version 1 specpr). Each of the 5 main data files (v, w, d, u, and y) may contain up to 9,999,999 records and may be assigned in the program to the named disc files or to magnetic tape drives. The starpack file contains a maximum of 50 extinction correction "starpacks" on disc. The philosophy behind single letter file IDs is to minimize user typing. After all, why type a 10 or more character file name every time you want to access a spectrum. In practice, users quickly learn this abbreviation method to associate a single letter with a data file.

(WARNING: some operating system limitations may preclude implementation of direct tape I/O--check with your local administrator.)

(WARNING: with a limit of 9,999,999 records per specpr file, large specpr files will not fit on most tapes.)

Error bars (1 sigma standard deviations) are stored in the next record after the data when generated. This saves room since many files do not contain error values. In this manual as well as in the program, the word "error" is used to mean the error bars: the errors to the data, and not program errors, user command errors, or input/output (I/O) errors. Input/output errors and user command errors will be referred to more specifically.

In Specpr, many spectra are contained in one data file. The alternative method is to put each spectrum in a single file, and other data processing systems do this. The disadvantage to one spectrum per file is that each file must be unique in name, so you must type in long or complicated names to get access to a particular spectrum. Also, rapid access to many spectra quickly (like a library search) would be slow with extra overhead to open and close each file. With many spectra in one file, the user can list the file and see long titles to recognize the spectrum he or she wants and then type just a few characters to access it. Access to any single spectrum or a group of spectra is very quick--no open or close is necessary, just a simple read or write.

Each I/O operation is analyzed for I/O errors by the program. If an I/O error occurs, the error encountered is listed on the CRT so the user can try to figure out what happened.

2.2.1 Deleted point values

All data values for "data" or "wavelength" (y or x data) points are valid except

-1.23x10+34

which is taken to be a deleted point.

2.2.2 General data file I/O

The user accesses a data array (spectrum) by typing in the File ID letter and the record number in the file. In general, a lower case letter means to read (or write) a particular data set. An upper case letter means read (write is not allowed in this context) the particular data set, but treat the data as horizontal axis values (the x values of x-y paired data). In the case of spectra, a capital letter would signify the wavelengths.

      Examples:    v23           # read data set in file v, at record 23.
                   w126 W15      # read data set w126 and read data set
                                   w15 as the "wavelengths" (or
                                   horizontal axis array).

Also, transfers between all combinations of v, w, d, u, y, and s are allowed if the user-selected file protection permits such transfers (see File Protection, section 2.3).

2.2.3 Transfer Restrictions

If the device names are equal, one of the special restrictions below will be applied. For instance, if the name of "Vfile" is the same as the name of the "Ufile" (e.g. a data tape is on MT0 as "Ufile" and is to be transferred to the "Vfile" on disc), the restriction applies to tape to disc, disc to tape, disc to disc, and tape to tape transfers. These restrictions are enforced in an effort to preserve the histories which refer to a specific spectrum by data tape name and record number (sometimes called file number).

Transfers to tape including disc to tape and tape to tape transfers must be to corresponding record numbers but do not have to begin with record 1 (if the data file names are equal).

Transfers of tape to disc, but not disc to disc, must begin with record number 1 (if the data file names are equal).

Transfers of disc to disc must be to corresponding record numbers but do not have to begin with record 1 (if the data file names are equal).

2.3 File Protection

All files may be totally or partially protected, or completely unprotected. The fourth line of the CRT header gives the protection status for all six devices (devices v, w, d, u, v, and s).

• If the protection number is positive or zero, the device is a read/write device where you can read up to and including the protection, but you can only write to the protection +1 record. For example, a value of 637 means you can read the first 637 records, and you can only write to record 638.

• A protection number of -1 means totally unprotected so you may read or write anywhere in the file randomly.

• A protection number of less than -1 means the device is a read-only device where you can read up to the absolute value protection number. For example, a value of -264 means 264 records are read only and you can’t write to the file.

You can set the protections on many files on one command line. Example:

v0 d-1 u432 y-600 w-600 s-50

where v0 means to protect 0 files on device v (write to file 1 only, 0 files can be read); u432 means to protect up to record 432 (write to record 433); y-600 means that y is a read-only device with 600 records; similarly for w; and s is a read-only file with 50 records. If the protection number is zero or positive, it is incremented each time the device is written to.

2.3.1 Use of SPECPR File Protection

The SPECPR file protection is designed to protect the user from destroying existing data and to allow use of the program with minimal thinking of where data is going (so the user can be thinking about the science). Protection should be used at all times unless there is some necessary reason for not using it. Remember that a mistake is what will destroy data in an unprotected file--and everyone makes mistakes.

The following is an example of the use of protection when using specpr tape I/O. Some groups have a different philosophy regarding specpr tapes. For example, at the U. S. Geological Survey, Denver spectroscopy laboratory, specpr tape I/O is not used. Instead, specpr files are kept on line on disk and written to tape only with normal system backups. In any event, the following example illustrates the proper use of protections to prevent data loss, as well as to maintain histories.

Start SPECPR. Say you have 2 tapes to be transferred to disc and then do some processing. Load the tapes (we will call them A01 and B01): A01 on MT0, and B01 on MT1. Plan to assign u to MT0, y to MT1, v and w to disk files. Set the protection on v and w to 0 (this is the default). Type in the names of the devices u and v = A01; y and w = B01. Assign the devices as noted above. Now here is where the protection comes in. First, let us transfer the tape on MT0 (A01 = u). The protection is -9999. Say on the label on the tape, there are 673 records--do not believe this. We could have set the protection to -673, but what if the last time you added stuff to the tape you forgot to update the number or someone else added stuff and did not update it? If that happened and you then added stuff after record 673 and wrote it back to the tape, someone might get very mad. So--let the computer find the end of the data. Go to file transfer and type "u1 + 9999tv1". All the records up to the end of file mark will be transferred. Say there were really 729 records on the tape. Then, after the transfer, the protection on v would be 729 and -9999 on u. Now transfer MT1 to the disc: "y1 + 1999tw1". Say there are 463 records on MT1. The protection after the transfer would be 463 on w and -9999 on y. Now go back to change protection routine and make the protection on u-729 and on y-463. All your data are fully protected.

Now say you did some processing and added 47 records to v and 21 to w. You must then transfer the stuff back to the tapes. Take the tape off MT0 and put in a write ring (if you had a write ring in before, you are asking for trouble). Go to the change protection routine and change the protection u from -729 to 729. If the tape was not at the load point when you put in the write ring, you must reset the record pointer in the program. This can be done in one of several ways: (1) change the tape name (change the name of u from A01 to A01 (yes, the same name); when the name is changed, the tape is rewound); (2) display record u1; or (3) transfer u1 to somewhere else (this is faster than a display). If d is assigned to disc and it is used as a workfile (protection = -1), transfer "u1td1" or "u1td1000". If d is assigned to /dev/null, it will read u1 before you get the "illegal transfer, device assigned to /dev/null" message.

Now that the tape record pointer is reset, you transfer your stuff from v to u. Type "v730 + 999tu730". Note 730 is one more than the current protection. The transfer will continue up to the protection limit on v (776), and after transferring v776 to u776 the message "FILE REQUEST GREATER THAN FILE PROTECTION" will come on--press return.

It is now a good idea to list the tape from just before the point at which data was added to the end of file to make sure the tape does not have any obvious errors.

Now you must transfer the stuff on w to the tape. Change the protection on u to 463; then change the name of u to B01 (this puts in the correct name and resets the record pointer). Now go to file transfer and type "w464 + 99tu464". The program will stop at the protection limit on w of 484, transferring the added 21 records. Now list the type as before to check the newly added records.

Following this method will maximize the safety of your data. Failure to do so will cause no sympathy from the person whose data you accidentally destroy (and you must recreate it for him or her).

The specpr protection is closely tied to the history philosophy of specpr. The specpr history uses the "tape name" and record number as a unique identifier for a spectrum. Proper use of the history mechanism necessitates proper protection. Don’t set the protection to -1 and write over data. Later data could be referencing specific records earlier in a file. For example if record 36 was a sample minus dark spectrum, and record 167 was record 36 divided by a standard, and then you wrote over 36 with another data set, then the history would be broken. Similarly, it is vital to keep file names indicative of the final archive source. Don’t do work in a file called "junk" or "temp" and then rename it XYZ001 because all histories will be referring to file "junk" or "temp" and you will have no idea what that file really was a year from now.

2.4 Command Interpretation

The specpr terminal input routine looks for various special characters in the input. These special characters are: <, >, ?, %, =, !, ;, {, [, and $. All of these characters except ; {, [, and $ have special meaning only when it is the first non-blank character on the line. Additional special character sequences are also interpreted: "\#", "\\#", "==", and "px(". If a "{" or "[" is found on the command then the corresponding bracket, "}" or "]", will also have a special meaning. The effect of these characters is as follows:

This character when followed by a file name causes specpr to read input from that file. You can also specify a starting and ending line number. For example

<inputcommands 20 40

will read commands from a file called inputcommands starting at line 20 and stopping after line 40 of the file. If the ending line number is omitted, the file will be read until the end of the file is reached. If the starting line number is also omitted the file is read starting at the first line. When commands are being read from an input file, that command file may read commands from another input file. That input file can then read from yet another file, up to 9 deep. In a sense, a command file could set several variables and read another command file similar to a subroutine. In this case, the "subroutine" has access to all variables, thus it is similar to subroutines used in the Basic programming language. When one command file finishes, commands are read from the next line of the previous command file. For example, given two command files:

file "a1" file "a2"
---------- ------------
line 1 line 1
line 2 line 2
<a2 line 3
line 4
<a2
line 6

then the command sequence would be as follows.

                 <a1     # terminal input from user
                 a1 line 1
                 a1 line 2
                 a2 line 1
                 a2 line 2
                 a2 line 3
                 a1 line 4
                 a2 line 1
                 a2 line 2
                 a2 line 3
                 a1 line 6
                 # back to terminal input

This character when followed by a file name causes specpr to copy
all user input into the named file. When not followed by a
file name it terminates the copying of the input.  Example:

                > outputfile     # copies all commands to file "outputfile"

                >                # turns off copying of commands to "outputfile"

This character when followed by any string will pass that string
to the UNIX shell (/bin/sh, see the UNIX manual) for execution.
For example typing

                !ls

will give you a listing of the files in the current directory.

A semicolon anywhere in an input line is treated as if the user
had typed a carriage return instead of a semicolon. For example
typing

                c;0 1

is equivalent to typing

                 c
                 0 1

The special characters ?, %, =, and $ involve the "command file" which automatically keeps a record of the last 20 commands the user has typed, and in addition can contain up to 80 permanent commands saved by the user. The commands in the command file are numbered 1 to 100 with commands 1-20 being the last twenty commands typed by the user and commands 21-100 being the permanent commands. The effect of these 4 special characters is as follows:

This character lists the contents of the command file on the user’s terminal. The commands are printed in five groups of twenty commands. If the ? is followed by a digit from 1 to 5 the corresponding group of commands will be printed. If no digit is specified, the first group of twenty commands is listed. For example,

?2

will list commands 21-40.

This command allows the user to type in the permanent commands. The = should be followed by the number of the command to be entered. The system will prompt the user with a question mark at which time the user should type in up to 80 characters for the new command. For example,

=25

allows the user to type in command 25.

This command allows the user to copy a command from one entry in the command file to another. Commands may be copied only from commands 1-20 to commands 21-100. For example

% 10 25

will copy command 10 to command 25.

This command when followed by a number from 1 to 100 extracts the corresponding entry from the command file. For example, if command 25 contains

0.574

then typing

0 $25

is equivalent to typing

0 0.574

Care is needed when the command number is followed by another number. If the command ends with a number then the user should follow the command number with a comma if the number following the command is part of the desired final number. For example, if command 25 contains

0.574

then typing

0 $25,7

is equivalent to typing

0 0.5747

while typing

0 $25 7

is equivalent to typing

0 0.574 7

is used to parse internal variables. See section 2.6.

is used to parse aliases. See section 2.5.

\# The character sequence "\#" means everything after and including these characters are comments and not to be interpreted by the command processor. If \# occurs as the first two characters on the command line, then the line is ignored.

\\# The character sequence \\# is an "escaped" comment meaning interpret the characters as \# and pass them to the command processor, in effect uncommenting the comment.

The character string == means an alias function follows. See section 2.5 below.

The character sequence "px(" means a pixel coordinate of the form px(i+j,k+l,m+n) where i, j, k, l, m, and n are integers describing an extraction from a 3D file. See section 6.2 for more details.

2.5 Alias Definitions and Substitutions While running specpr, an alias list of common commands can be created using this option. This is used to reduce the amount of typing needed by substituting short alias words for long commands. Alias words can be created for any type of command used in specpr. These alias words can either be read into specpr from a file or set up every time specpr is run.

2.5.1 Creating Alias Words Alias words can be created for any command used in specpr. These alias words are defined by typing ==[alias word] translation. The alias word must be inside square brackets and followed by its translation. An alias word can consist of any letters or numbers inside square brackets. If you use four or more capital letters, you do not need to use square brackets when you type the alias. At any point in the program specpr, an alias word can be defined or translated.

EXAMPLES ==[hi] hello This sets the alias word ’hi’ to
translate into ’hello’
==[DIRL] !ls This sets the alias word ’DIRL’ to
give a listing of the current directory

2.5.2 Translating Alias Words For an alias word to be translated, it must either be inside square brackets or be one word of four or more capital letters. The alias word can be entered at any point in the program and the translation will take place. The line will be reprinted on the screen showing the translation and then executing the command.

EXAMPLES

[hi]

The alias word is translated into hello

hello

DIRL

This alias word does not need brackets

because it consists of four capital letters.

!ls

It translates into this command which then

will execute a listing of the current directory

2.5.3 Listing and Saving Alias Words and Translations The current list of alias words and translations is printed onto the screen using the command

==list

as the only character sequence on the command line. If a filename is typed after the list command, the list of alias words and translations will be saved in the specified file.

EXAMPLES

==list

This lists all the alias words

onto the screen

==[hi] hello

==[DIRL] !ls

==list alias.list This saves all the alias words and

translations in the file alias.list

2.5.4 Reading Alias Words into specpr from a File To read a file of saved alias words and translations into specpr, type < and the filename. This will allow all the alias words in the file to be used in specpr.

EXAMPLE

<alias.list

This reads the alias words

and translations from the
file alias.list into specpr

==[hi] hello

==[DIRL] !ls

2.5.5 Deleting or Writing Over an Alias Word An alias word can be deleted by entering ==![alias word] anywhere in specpr. This will not delete it from a file of stored alias words unless the alias list is resaved into the file. An old alias can be overwritten by redefining the same alias word. The list must also be resaved for this alias translation to be changed in the file.

EXAMPLE

==![DIRL]

This deletes the alias word DIRL

and its translation from the list

2.6 Variable Parsing Variable parsing is done on strings enclosed in curly braces "{}". Variables may be set, incremented, decremented, or other simple math may be performed and the result inserted in place of the curly brackets on the command line. Variable parsing is useful in specpr command files. The variable parsing routine has a limited understanding of math functions and variable parsing. The variables currently incorporated are:

ia-iz -- 26 user integer variables
ra-rz -- 26 user real variables (floating point)
iprtv -- protection of file v,
iprtw -- protection of file w,
iprtd -- protection of file d,
iprtu -- protection of file u,
iprty -- protection of file y,

The routines only understand the math functions of equivalence and addition (although addition of negative numbers is allowed). Here are a few examples of valid variable substitution strings.

   {iprtv}        # replaced with the protection of device "v"

{ib=54}

# not replaced (sets ib to 54)
{ib+-5}

# replace with 49 (ib=54-5) (addition of negative numbers)
{ib=ib+iprtv}

# not replaced, (sets ib)
{ra+2.3+-6.5}

# replaced with -4.2 (user variables are initialized to zero)
{2056+1123+-43+iprtd+ia+ib}

# (Only limit is 80 characters per line)

NOTE: a minus in front of a variable, such as "{-ib}" will not work.

2.7 Order of Substitution and Command Interpretation In specpr, the order of the interpretation of the special characters is $ substitution, {, ;, ?, ==, =, %, >, !, <, alias translation, and \#. Any of these special characters can be used in an alias translation because the program loops back to the beginning when a translation is performed. The special characters would then be interpreted the second time through the loop. This program would continue looping until all of the translations are finished. The $ substitutions can contain alias words because the translation takes place after the $ substitution is done. Both the $ substitutions and the alias translations can contain ; which are later processed. However, the \# comment statement can not contain a ";" because it is processed before the comment statement is found and everything after the ; would be stripped off for the next command. The flow chart below shows the order of these command interpretations.

EXAMPLES  ==[lv] lv;;;0 99        Assigning this alias would
                                        give the list command, return
                                        three lines,and list from 0
                                        to 99

==[lst] $21 This would assign the alias lst to

the command in file number 21
If 21 has [DIRL] in it, the alias
would translate to !ls

2.7.1 Flow Chart for Command Interpretation Order

 ____________
| input line |             command
|____________|               file     alias   $ sub.            copy to
     |      var p.  return   list      def.     def.     copy     file
  ___|___    ___     ___      ___      ____      ___      ___      ___
 |   $   |  |   |   |   |    |   |    |    |    |   |    |   |    |   |
 | subs. |->| { |-->| ; |--->| ? |--->| == |--->| = |--->| % |--->| > |
 |_______|  |___|   |___|    |___|    |____|    |___|    |___|    |___|
     ^                                                              |
     |                                                              |
     |                          _______      ___      ___           |
     |       alias translation | alias |    |   |    |   |          |
      ---------<---------------| trans |<---| < |<---| ! |<---------
                    done       |_______|    |___|    |___|
                          no alias |         read     UNIX
                      ____  trans. |         from
          _____      |    |  done  |         file
         | end |<----| \# |<-------
         |_____|     |____|
                    comment

2.8 Specpr File Types and Content The specpr I/O routines support multiple file types. There are "standard specpr files" and other files. Currently, the other file types include 3-dimensional image type files, which me be Band Interleaved by Line (BIL), Band Interleaved by Pixel (BIP), or Band SeQuential (BSQ) files, with any header size, with any data type. Currently routines exist that read 16-bit integer (I*2) 32-bit integer (I*4) and and 32-bit real (Real*4) data, but others can be added. It turns out that this general I/O package can read just about any format, because a 3D file can also access a 2D or 1D file since the higher dimensions have a dimension of 1. The standard specpr record, however, is optimized for x-y paired data.

2.8.1 The Standard Specpr File Content Specpr files are random access files, 1536 bytes per record. The data types are described in the file format document in the specpr programmers notes. Currently, there are four basic types of data formats (although many more can be easily defined for specific disciplines):

1) beginning spectrum (512 bytes of header and 256 channels),
2) continuation records for spectra with more than 256 data channels,
3) character records where the data space is ascii text, and
4) text continuation text records.

A data set can consist of as little as a single record (a single one-dimensional array) or have up to 12 continuation records (there is planned expansion to substantially increase the number of continuation records). A spectrum typically consists of a wavelength set, data (e.g. reflectance) and the error bar. In specpr a data set is only one array, not three (e.g. waves, reflectance and error). The wavelengths are kept in an independent record. The error bars are kept in the record after the data values. Some data do not have error bars, so space is saved. A sample specpr file might look like this to the user (this is extracted from an actual data file):

Table 2-1

-------------------------------------------------------------------------------
record title channels time date
-------------------------------------------------------------------------------
0 reserved for future: intended for file
description. This record has no user
access.

1 ************ SPLIB001 ****************** 36 Characters of TEXT
.
. other data records
.
15 USGS Denver Beckman STD wavelengths 1x 512 02:57:26.00 10/15/1985
17 USGS Denver BKMN 1x resolution 512 02:57:26.00 10/15/1985
.
. other data records
.
73 Description of Alunite Hunt 295.?B 3132 Characters of TEXT
76 Alunite 295.3B .2-3um 1x ABS REF 512 12:03:14.00 08/20/1985
78 errors to previous record 76 512 12:03:14.00 08/20/1985
80 Alunite 295.3B .9-2.6um 2x ABS REF 680 09:49:27.00 08/21/1985
83 errors to previous record 80 680 09:49:27.00 08/21/1985
.
.
.
-------------------------------------------------------------------------------

In the case of record 76, the number of data channels is more than 256, so one continuation record is used (record 77; hidden from user view). Similarly, records 16, 18, 74, 75, 79, 81 and 82 are continuation records. The following table shows how the data are spread over continuation records:

Table 2-2

-------------------------------------------------------------
Continuation number of channels Data channel range
record number in record
-------------------------------------------------------------
- 256 1 - 256
1 383 257 - 639
2 383 640 - 1022
3 383 1023 - 1405
4 383 1406 - 1788

5 383 1789 - 2171
6 383 2172 - 2554
7 383 2555 - 2937
8 383 2938 - 3320

9 383 3321 - 3703
10 383 3704 - 4086
11 383 4087 - 4469
12 383 4470 - 4852
-------------------------------------------------------------

The following table shows how text data are spread over continuation records. Note that there is also a pointer to additional text, so the real text size is limited only by disk space.

Table 2-3

-------------------------------------------------------------
Continuation number of characters Character range
record number in record
-------------------------------------------------------------
- 1476 1 - 1476
1 1532 1477 - 3008
2 1532 3009 - 4540
3 1532 4541 - 6072
4 1532 6073 - 7604

5 1532 7605 - 9136
6 1532 9137 - 10668
7 1532 10669 - 12200
8 1532 12201 - 13732

9 1532 13733 - 15264
10 1532 15265 - 16796
11 1532 16797 - 18328
12 1532 18329 - 19860
-------------------------------------------------------------

2.9 "Wavelengths" and Other Concepts of x-y Paired Data "Wavelengths" and other axes are simply a data set and a label in specpr. The default label for the "x-axis" is "Wavelengths (microns)" and any data set in the specpr data files can be used as the x-axis values. The x-axis label can be changed to something else by changing the fourth line of the manual history of the x-axis data record to: "\W string" where "string" is the character string for the label.

Example:      v23V19     # the data set is v23, the x-axis values
                           are in record v19 (specified as a capital
                           letter file id).

Then if the fourth line of the manual history is:

           \W Intensity (seconds)

the crt plot would label the horizontal axis "Intensity (seconds)". There is a special case for specifying a wavelength set: instead of a file ID, use a capital c, "C", and the number of channels and the x-axis values will be set equal to the channel number.

Example:          C236     sets the x-axis values to 1 in channel 1,
                           2 in channel 2, etc., to 236 in
                           channel 236.

A data set can be called up with wavelengths specified by the data set if the wavelength pointer is set in the header info to that particular data set. For example, if v23 has its wavelength pointer set to 19, then the default x-axis data set is in record 19 of the same data file. The default x-axis values are found by specifying the character "&" instead of the upper case file ID and record number. Then

                    v23V19
and
                    v23&

are equivalent.

2.10 Help! Specpr has a help facility where you may type the word help on the command line at any point and go to the help routines. You may also type help and a key word to get help on a particular subject. The help command with no keyword will show you a list of key words to choose from. See Chapter 3 for more details.