The Commodore 899D calculator, released in 1976, is a unique model that combines practical functionality with an interesting aesthetic design. This calculator’s sturdy build and range of capabilities made it an attractive option in its time, especially for users who wanted basic but versatile computational tools.
The device measures approximately 75mm (width) by 147mm (height) by 25mm (depth) and weighs around 112 grams without batteries, making it lightweight and easy to carry. It is powered by a 9V DC PP3 battery and can also be connected to an adapter using a socket located on the top right. The case is made of cream-colored plastic with a matte finish, featuring a distinctive black keyboard surround. The calculator’s keyboard includes brightly colored keys typical of Commodore products, giving it a recognizable look. However, users have noted that the keys, while positive in feedback, feel slightly squishy. A red plastic display filter slopes to provide a clear LED display, albeit with limited viewing angles. Commodore’s logo appears in black on a metallic sticker that fits neatly into a recessed slot on the device’s top section.
The display on the Commodore 899D is an eight-digit red LED with a ninth digit used for indicators, including error, memory, and negative signs. This LED “bubble lens” gives the calculator a vintage aesthetic common in 1970s electronics. Its functionality includes four standard arithmetic operations, as well as additional keys for percentages, reciprocal, squares, square roots, changing sign, and a memory function. The calculator also provides parentheses for grouped calculations and a register exchange function for more complex operations. However, a notable limitation is the mutual exclusivity of the parentheses and memory functions; if one is in use, the other cannot be engaged simultaneously.
Under the hood, the 899D is built with Commodore’s 3D-31-2A CPU paired with a nine-digit LED display module. The calculator’s keyboard board is securely fastened to the front with ten screws and connects to the main CPU board via a ribbon cable. To open the case, the user removes two rear screws and uses a screwdriver to carefully disengage the plastic lugs, allowing the back cover to hinge open.
Logic
- (C/CE): Press once to clear the last entry and a second time to reset the calculator.
- Automatic constant: Available across all four functions.
- Input overflow: Suppressed; a ninth digit entry is ignored.
- Negative numbers: Shown with a “-” sign in the leftmost digit.
- Divide by zero: Displays “E00000000” and can be reset by dividing by one.
- Overflow: Indicated by “E” in the leftmost digit, resettable by successive division by 10.
- Negative square roots: Display “E00000000” and the initial number.
- Memory: Signaled by the far-left decimal point.
- (MT): Clears memory after totaling, while (X-M) exchanges the memory with the current register.
- (X-Y): Swaps the current display with the register.
- Square root of 99,999,999: Displays 9999.999, truncating one digit.
- Percentage key: Divides result by 100 and can also correct overflows.
The Commodore 899D stands out as a sturdy, functionally rich calculator with a nostalgic aesthetic. Its limitations, including the “Nines Square Root” issue and restricted simultaneous use of memory and parentheses, reflect its vintage nature, but its construction and useful features make it a noteworthy piece for enthusiasts of classic computing devices.
