The Decimo Handy calculator, introduced in 1976, is a compact, palm-sized device designed for basic arithmetic functions. It has the model number 508A. Manufactured in Singapore, this calculator features a sleek, one-piece white matte plastic case with a black gloss/matte section that encompasses the top, front, and keyboard surround. The design includes a raised, ridged area with a silver-painted panel displaying the brand and model name. The display filter is a tilted red plastic with a linear convex shape, providing a large, bright display with a limited viewing angle.
The calculator is powered by a 9V DC PP3 size battery and has a socket on the top side for an adapter. It weighs approximately 84 grams without batteries and measures about 72mm x 107mm x 21mm (width, height, depth). The keys offer short travel with a positive click and individual escutcheons, enhancing the tactile feedback.
The Decimo Handy calculator features an 8-digit red LED display with individual bubble lenses. Although there is a ninth digit physically present, it is never used. The calculator supports standard four functions with percentages, making it suitable for everyday calculations.
Logic:
- The “(C)” function cancels the last number entered; pressing it twice clears the entire calculator.
- Input overflow is suppressed; entering a ninth digit is ignored.
- Negative numbers are displayed with a “-” in the leftmost digit, limiting negative numbers to seven digits.
- Automatic constant is available for all four functions.
- Overflow results in all decimal points lighting up, recoverable using “(C)”.
- Divide by zero displays “…….0.” and is not recoverable.
- The calculator has a divide to minus zero bug: entering (-)(1)(/)(1)(0)(=) results in “-0.1”, and continuing to press (=) eventually leads to “-0.”.
The original case for the Decimo Handy is made of soft black plastic with square edges, an open top, and half-moon cut-outs on either side. The calculator’s internal components include a CPU with a square spiral logo (C683 7610), an IC from National Semiconductor (DS8871N 617), a 9-digit red LED display unit with a bubble lens (National Semiconductor A1185B 540), nine resistors, and one capacitor. The keyboard assembly sits on top of the main CPU board and is connected with 15 strong wires. Disassembly involves removing a small screw from the back, allowing the black section and the entire inside assembly to slide up.
The Decimo Handy calculator is a compact device with an attractive layout, though its logic has some limitations, including inconsistent recovery, seven-digit negative numbers, and a divide to minus zero bug. There was at least one other model in this range, the Handy M.
