The Aristo M65 is a handheld calculator from the mid-1970s manufactured by the German company Aristo, known for its slide rules. With its sturdy construction and bright red LED display, the M65 exemplified the build quality and innovation of 1970s electronics.
The M65 measures about 6.2 x 15 x 2 cm and weighs 148 grams with its protective plastic cover. Despite its portable size, the M65 feels substantial, with a glossy white plastic base and black plastic front. The eight-digit display uses individual large LEDs for clarity. A slide switch changes between a floating decimal point and fixed two-digit mode to support calculations in pounds, shillings, and pence.
Inside, the M65 uses integrated circuits from major European manufacturers. The logic is based around an unbranded Rockwell chip, supplemented by ICs from ITT. High-quality components like tantalum capacitors demonstrate the premium design.
With four basic functions, percent, square root, and a five-register memory, the M65 had capabilities similar to competing models. Clever design elements enhance usability, like the two-key “function” prefix for advanced operations. The exchange key swaps the display with either the memory or previous number entered.
Despite relatively robust logic, the M65 does suffer from the “pseudo-fixed decimal point” issue common in 1970s calculators. After entering a number with decimals, additional digits revert to zeroes until an operation forces re-evaluation. Still, the M65 represents an appealing combination of style, quality, and functionality that makes it a classic 1970s calculator.