This white and black battery-operated calculator has number entry keys, arithmetic function keys, and memory function keys. It also has a clear entry/clear key, a percent key, and an EX key, as well as a decimal point key. There is a nine-digit display. The non-printing device has a sealed, rechargeable battery.
A mark behind the keyboard reads: aPF MARK 21 (/) Electronic Memory Calculator. A plaque on the back gives operating instructions. A mark on it reads: MARK 21 (/) Model No. Another mark on it reads: R-009175 (/) Serial Number. Another mark there reads: APF ELECTRONICS (/) NEW YORK, N.Y. 10022 (/) MADE IN JAPAN. A very small mark in the bottom corner of the plaque reads: 215901.
An October 1976 advertisement in the New York Times lists the APF Mark 21 as regularly priced at $24.99 and on sale for $19. An April 1977 ad in the Los Angeles Times lists the APF Mark 21 as selling regularly for $19.99 and available, with the exchange of any calculator, for a sale price of $14.99.
References:
Los Angeles Times, April 13, 1977, p. A10.
New York Times, October 17, 1976, p. 380.
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