APF Mark 55 Handheld Electronic Calculator

This handheld electronic calculator is designed for scientific work. It has an array of digit keys with a decimal point key, keys for the four arithmetic functions, a sign change key, a reverse x and y key, a down key, an ENT key, and an EE key. At the top are shift, recall, standard deviation, natural log, and clear display keys. Below these are sine, cosine, tangent, summation, and power keys. The function keys all can assume a second function, allowing for evaluation of hyperbolic trigonometric function, decimal logarithms, mean values, square roots, and so forth. A few keys are devoted to converting decimal and standard units of weight and measure—centigrade and Fahrenheit temperatures, liters and gallons, centimeters and inches, and kilograms and pounds.

The ten-digit LED display is behind the keyboard. The device has space for a nickel/cadmium battery behind this, as well as an outlet for an adapter/charger.

A mark above the keyboard, even with the on/off switch, reads: aPF MARK 55. A mark on the sticker on the back of the case reads: aPF mark 55 (/) ADVANCED SCIENTIFIC CALCULATOR. After brief operating instructions, futher marks read: MARK 55 (/) Model No.; J-036646 (/) Serial No.; and: APF ELECTRONICS INC. (/) NEW YORK, N.Y. 10022 (/) MADE IN JAPAN.

A March, 1976, advertisement compared the features of the APF Mark 55 with those of the HP-45, noting that both calculators used reverse Polish notation for data entry, carried out a wide array of operations, and could store and recall nine registers of numbers. According to the advertisement, the HP-45 cost $195 while the APG Mark 55 cost only $79.95.

References:

Los Angeles Times, March 14, 1976, p. V57.

Los Angeles Times, June 8, 1976, p. 9.

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