The Commodore SR7919 calculator, released in 1976, was part of Commodore’s scientific line of calculators. Manufactured in the United Kingdom, this calculator features a distinctive two-piece beige and black plastic case with a top-heavy design to accommodate its 9V battery.
The SR7919 measures approximately 62mm x 135mm x 23mm and weighs 82 grams without batteries, it features a stippled black plastic keyboard surround. The calculator’s keys, while somewhat wobbly, are made distinctive by their metallic blue and red on silver design, which indicates double functions. The branding includes a raised silver-painted logo on top and a black printed metallic label below the display.
The display itself consists of 8 red LED digits with bubble lenses, plus a ninth digit for displaying negative numbers, function selection, and error indicators. A convex red plastic filter enhances the display’s brightness, though it does limit the viewing angle.
Under the hood, the SR7919 is powered by a MOS MCS 7529 CPU manufactured in week 26 of 1976, alongside an ITT 548-5N IC from week 23 of the same year. The internal components are relatively simple, consisting of a 9-digit LED unit with individual bubble lenses, one capacitor, and one resistor. The main CPU board (Part No. 200826) connects to the keyboard assembly via a 16-way ribbon cable.
The calculator offers standard mathematical functions including trigonometry, squares, square root, reciprocal, logarithms, powers, and pi. It features a 5+2 scientific display mode with full eight-digit mantissa and includes three-function memory capabilities. The device runs on 9V DC power, accepting a PP3 size battery or an external adapter through a side socket. It includes a power-save function that activates after approximately 25 seconds of inactivity.
Logic:
- C/CE button clears last entry on first press, entire calculator on second press
- Power-down mode activates after 30 seconds, showing underscore in ninth digit
- Ninth digit input is ignored when typing numbers
- Overflow errors show “r” (positive) or “F” (negative) in ninth digit and cannot be recovered
- Function key use indicated by ninth decimal point
- No visual indication of memory storage
- No constant function available
- 8-5 button displays eight most significant places of exponential numbers
- Negative numbers shown with “-” in ninth digit
- Memory overflow maintains original number
- Negative square roots not allowed and show unrecoverable error
- Change sign operator works during number input
The SR7919 offers straightforward functionality in a distinctive design, though it has some limitations like slow computation times for complex functions and lack of overflow recovery. Its unique double-function buttons and metallic details set it apart from typical Commodore calculators of the era, which often featured more crowded keyboard layouts.
