Casio Mini CM-605

Casio CM-605 Mini Calculator

The Casio Mini CM-605 was a compact horizontal format calculator produced by Casio Computer Company Ltd. in 1974. Measuring approximately 146mm x 72mm x 30mm and weighing 162g without batteries, this two-piece black and white plastic casing housed a 4 function calculator with a 6-digit blue VFD display. The display featured a unique representation of zero, using only the lower half of the digit.

The calculator was powered by 4 AA batteries or an optional AC adapter (AD-4145, 0.18W, center negative). The long travel keys had a soft click on return, and the raised display section was slightly tilted for better viewing.

Inside, the calculator utilized a NEC μPD178C K43166 28-pin DIL CPU, a single NEC LD8097 6-digit VFD tube, 13 capacitors, 3 resistors, 3 resistor arrays, and a Fuji UT 0627A 4E-06 transformer unit, likely housing transistors and diodes for power supply generation.

The keyboard assembly (6S-E4B) was attached to the front case with five screws, and the main board (6S-1B) sat on top, held in place by three plastic posts and the power adapter socket, with the two joined by 10 strong wires.


  • The (C) button cleared the last entry, while (AC) cleared the entire calculator.
  • Overflow on number input was suppressed, ignoring the seventh digit.
  • Overflows displayed the result but locked the calculator, except for the display shift function, and were not recoverable.
  • Negative numbers displayed the “-” sign on the far right (first) digit of the least significant 6 digits.
  • Divide by zero showed all zeros with a shift display of “nxxxxx”, where n was the starting number, and the remaining digits showed a counting clock.
  • Automatic constant was available for all four functions.
  • Negative numbers were limited to five digits, with the “-” sign in the far left (sixth) digit. The shift key allowed viewing up to twelve digits, but the negative sign moved to the first digit.
  • The shift key (>) showed the least significant six digits for the product or quotient.
  • The calculator suffered from the negative zero bug and the divide to negative zero bug.

The Casio Mini CM-605 was a basic yet compact calculator with a unique display and early logic, showcasing Casio’s foray into pocket-sized calculators, albeit with some limitations and bugs.

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