Notes:

A calculator designed by Clive Sinclair’s famous English brand for
cars, computers and calculators. Made in England.
This calculator is very different from any other scientific
programmable RPN calculator I have ever seen. It is simply impossible
to use it without first reading its 16page manual. It took me a good
five minutes to figure out how to even multiply two numbers when I first
held it in my hands.
It is a calculator with some very peculiar features:
 The calculator has a 9 segment display. The first segment is
used for the negative sign, the last three for the exponent and
its sign.
 Values are always displayed using scientific notation. So, the
number "42" will be displayed as "4.2000 1".
 After the first value (as common with RPN calculators) the
"enter" key must be pressed. Since the "enter"key is above the
"0"key, the "▲"key (shift) needs to be pressed first. So,
when multiplying 6 by 9 one needs to press: "6", "▲", "0"
(="enter"), "9", "×".
 According to the manual using "enter" is mandatory. I have
however found out that the "+"key can be used as well, so to
calculate 6 x 9 one can also press: "6", "+", "9", "×". This works
because the first "+" adds 6 to the 0 on the stack. Only works
when the "C/CE"key is pressed first.
 There is just one stack position.
 Some keys have multiple functions. For instance, after
pressing "6", "▲", "0" (="enter"), pressing the "x"key will
display the square of 6.
 Entering negative numbers needs some training. For instance,
the number "5", at the start of a calculation (after first
pressing the "C/CE"key) can be entered by pressing "5" followed
by pressing "". This also probably works because this substracts 5 from
the 0 on the stack. When in the middle of a calculation one needs
to press "▲" and "" to negate a number.
 One key is really special, the "./EE/"key. What it does
depends on how many times you press it. Press once to type
decimals. Press twice to enter the exponent, press three times to
change the sign of the exponent to negative.
 Division by zero gives the result "0.0000".
 Square roots of negative numbers display the root of their
nonnegative value. Same for logarithms.
 Considering trigonometric functions. The calculator has
Radiansbased "sin", "cos" and "artan". The manual explains how to
calculate "arcsin", "arccos" and "tan" using formulae. Since the
calculator is programmable the manual also mentions that "A
program can be written to provide any of these functions as a
single keystroke operation."
 The accepted input values for "sin" and "cos" must be between
0 and π/2. Other values might produce (unpredictable?) results
or will hang the calculator.
Now, programming. The calculator has 24 programming steps. All
programs must start and end by pressing the "B/E"key (Begin/End).
When entering a program, the number keys perform their shifted
functions. Use the "var"key to display a value. To enter a number
(integer! no decimals allowed) one presses the
"‘’"key before and after the number. So, to
enter a simple program to multiply any number by five, enter:
"C/CE", "B/E", "0" (="enter"), "‘’", "5",
"‘’", "×", "▲" (="var"), and "B/E". Press
the "C/CE"key to leave programming mode. Press any number
followed by the "exec"key to now multiply it by 5.
All in all it is quite a feat to produce a small pocket size
programmable calculator. I still remember seeing Tandy’s version,
the Radio Shack EC‑4001 in a Tandy catalogue and being
utterly amazed by it. So capable with so few buttons! Takes some
getting used to however.
A nice writeup on Clive Sinclair and the Pocket calculator can be read
on this vintagecalculators.com page (link valid 20240113).
Many thanks to Richard Pilkington of the University of Salford for donating
this calculator to the museum.
