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A big bundle of material from
Hewson arrived at my home,
and I spent a long weekend
working through it. The
products I looked at. and their
prices, were the book 'Hints
and Tips for the ZX81'
(£4.2 5) Space Intruders
(£5.95), Language Dictionary
(£3.75) and Planet Lander
(£3.75).
The area covered by the
hints and tips book is shown
clearly by the chapter titles:
Saving Space; Understanding
the Display File; Converting
2X80 Programs; Chaining
Programs; Machine Code; plus
a mixed bag of twelve 1 K
programs.
The book appears to be
aimed mainly at those with
only 1 K RAM. if you have only
1K, I'm sure you realise how
difficult it is to run even the
smallest of programs.
Therefore it is essential to
understand how your ZX81
works, and know some short
cuts to help you in
programming. This book
should help you. 'Hints and
Tips' contains an extensive
2 7-page chapter on machine
code, although it doesn't give
a full list of codes. Hewson
Consultants do supply, for
£1.45, a full list, in which
each Op Code is explained and
cross-referenced. The book
eases the user into the idea of
using machine code, with
many examples of its use in
the book.
As well as this, I found the
chapter on chaining programs
quite enlightening. I didn't
know, until 1 read it here, that
it was possible to pass data
between programs. In all, this
slim volume is good value, and
an essential aid to those with
an unexpanded ZX81.
Space intruders
This program, for a ZX81 with
16K, comes dubbed once on
each side of a cassette, along
with full instructions. Even if
you'd never used a ZX81
before you got this program,
the instructions would enable
you to load and use the
computer. Written in machine
code for fast action, the
program has 40 alien ships in
each squadron, three laser
guns and full score display. As
well as this, the ZX81 can
play itself — although not very
successfully. Continuous firing
is available, and you have to
be quite quick to avoid the
aliens' bombs. All in all, this is
an enjoyable version of the
popular arcade game.
Language
Dictionary
ill!
Hit
Written for a ZX81 with 1 6K,
Language Dictionary is an
easy-to-use program, with a
number of options. It can
search for a word in either of
the languages used, allows
you to update or dump the
entire contents or to save
these on cassette. Although
the method used to store the
words packs them tightly it
appears it would take a long
time to find a word stored near
the end when the dictionary
was full.
Statistics
This pack consists of three 1 K
programs — Graph Plot, which
does exactly as the title
suggests, .using data entered
from the keyboard; Chi
Squared Test, which
"calculates the value of the
chi squared statistics for
comparing observed and
expected values"; and
Statistics, Regression, Trend
which is used to calculate
mean and standard deviation
and a least squares regression
line or trend line. I am sorry to
say that these programs
appear to do little more than
someone with a pocket
calculator and a piece of graph
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paper could achieve — and
probably in less time than it
takes to locate and load the
required program. Of course, it
would be valuable if a large
number of similar problems
had to be worked through. At
the very least, the programs
prove convincingly that the
ZX81 can be used for more
than games. Perhaps a 16K
maths tape would be more
useful, and would provide a
better indicator of the ZX81 's
abilities.
Planet Lander
This tape contains four 1K
programs. In Planet Lander
you have to (yawn) land your
spacecraft on a planet's
surface. Stopwatch is selfexplanatory.
The third
program is Space Docking, in
which (yawn again) you have
to dock your spacecraft with
the space station. The final
program is Clock, in which you
set the time and then sit back
and watch the display
increments each five seconds.
Two of these programs are
available from the book Hints
and Tips' so I suggest you buy
the book. You'll learn a fair
amount, and enjoy using the
book far more than you will
this last pack.
ZX COMPUTING SUMMER 1982 113