Elliott 903 Algol plotting procedures
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                            13-JAN-2001

If you are starting from scratch you need to download both
SIM900AL.ZIP and the new PLOTAL.ZIP. Between them they have all the
readme files. Although PLOTAL contains, as it were, the "plotter
hardware" and library procedures for plotting, the Algol compiler
has not changed and is therefore not included.

The plotter hardware is, of course, the VDU screen and was
developed on a VGA graphics system. Maybe it will not run on your
VDU and, if so, you could contact me (see end of MANUAL3.TXT) and I
might be able to prepare a version which does.

To install plotting just overwrite some old files with these three
new ones namely "LIBRARY.DAT", SIM900AL.EXE" and "SIM900AL.ADA".

There are several demonstration programs. "CORNU.DAT" draws a
Cornu spiral. "SUNDIAL.DAT" plots a graph showing sundial timekeeping
throughout a year and is faster to run. "NAVIG.DAT" plots the
ellipses within which a ship is likely to lie with various
probabilities, given four position lines from star sights. "MOON.DAT"
draws the Apollo 8 journey in 1968 under simplifying assumptions, but
runs very slowly; you are advised to run "MOONQUIK.DAT" instead.
"LOOP.DAT" shows the path of an aeroplane doing a loop the loop, again
under simplyfing assumptions. "WALK.DAT" just does a random walk of
1000 steps.

Plotting is in pixel units instead of in plotter steps.

The resident procedures like COS and SIN did not include the
plotter material because of its size, therefore plotting programs
had to be translated in library mode. This is also the case with
the simulator.

The procedure, SETORIGIN (see manual3.doc), has a different and
more appropriate action; its two parameters, X and Y, determine
the pixel count from the left and from the top of the screen to
the origin of plotting coordinates. If not used then the default
values are 320 and 160 which place the origin in the middle of
some VDUs.

The DOS manual says that to print the screen you first give the
graphics command and then type SHIFT+PRINTSCREEN, but this did not
always work for me.

DGNH