The Commodore PR 100 calculator, introduced in the late 1970s, has a slightly different look from other Commodore calculators of that era. It was manufactured by Commodore Electronic Calculators in England. The PR 100 features a distinctive two-piece stippled chocolate-brown plastic case, a departure from Commodore’s typical primary color schemes.
The keys, in shades of chocolate brown, light brown, caramel, and white, are flecked with gold coloring and offer a soft-click action. Above each key, an extra function label is raised and painted gold, giving it a unique look. The red plastic display filter is flat, slightly raised, and lightly tilted, providing a large image but a limited viewing angle for the digits.
Powered by internal rechargeable batteries, the PR 100 can be charged using adaptors 640, 707, 708, or 709 through a socket on the top side. A charge time of three hours provides approximately two to three hours of usage. The calculator’s dimensions are approximately 77.5mm in width, 158mm in height, and 31mm in depth, with a weight of 210g including the batteries.
The PR 100 boasts a 12-digit red LED display with a bubble lens, operating in an 8+2 scientific mode with two extra digits for negative and error indication. Its features include standard four functions, square root, reciprocal, pi, squares, factorial (including permutations and combinations), sign change, percentages, conversions, register exchange, integer, parenthesis (4), six function memory, trig and transcendental functions, DRG, statistics and graphical functions, sexagesimal base (HMS rather than DMS), fixed decimal mode, engineering mode, ten memories, and fractions. The calculator is programmable with 72 steps and ten registers.
There are two case versions of the PR 100, one similar to the P50 and a boxier version that may be specific to Europe, with suggestions that it was used for release to OEMs. The calculator’s functions are considerable, but it lacks recovery options, and the default two fixed decimal mode can be inconvenient.
To access the internal components, remove the two screws from the back, allowing the back section to lift off easily, hinging from the bottom.
Logic:
- The (C/CE) key cancels the last number entered when used once and clears the entire calculator when used twice. (CA) clears all working registers.
- Input overflow is suppressed; inputting a ninth digit is ignored.
- Automatic constant is available on all four functions.
- Negative numbers are displayed with a “-” in the far left (twelfth) digit, allowing full eight-digit negative numbers.
- The change sign key can be used mid-number entry, including for the exponent.
- Overflow and divide by zero errors show a tall “r” (or “F” if negative) in the far left digit and are not recoverable.
- Negative square roots result in an overflow with no recovery.
- Memory functions include (M)(#) to store and (MR)(#) to recall, where # = 0-9, with no indication of memory store.
- A three-way switch toggles between Clear, Run, and Load modes for programming.
- Fixed decimal points can be set using (F)(FP)(#), where # is 0-7, defaulting to two digits at switch-on.
- Engineering mode displays 3+# digits in the mantissa plus an exponent showing the nearest power of three.
- Scientific mode displays eight mantissa and two exponent digits, with two extra digits for negative indication. Internal precision is 10 digits.
Overall, the Commodore PR 100 calculator is an interesting calculator. It has a rich set of features for a calculator from the late 1970s and its unique design and good functionality make it a collectible piece of technological history.
