Unitrex Scientific 21 Handheld Electronic Calculator

This handheld scientific calculator has a black and off-white plastic case with an array of twenty rectangular plastic keys with rounded corners. Many of the keys have dual functions, one indicated on the key and one above it. Hence the ten digit keys also may represent three trigonometric functions, three inverse trigonometric functions, square root, natural log, exponent, and pi. The decimal point key may represent an inverse function while the EE (enter exponent) key also denotes clear number. The red function key is pressed to activate these secondary functions. It also serves to clear functions. Three of the four arithmetic function keys, as well as the total key, serve as memory keys. The calculator also has clear memory and clear keys.

Behind the keys is the on/off switch. Behind it is an eight-digit green vacuum fluorescent display. Text on the display cover reads: UNITREX (/) Scientific 21.

The back of the calculator has a compartment for two “penlight” batteries at the top. A sticker below give operating instructions. It also reads in part: MADE IN THAILAND.

Unitrex had sold a scientific calculator as early as March, 1974,, when it offered the Unitrex 80SR as competition for the HP-35, but at a much lower price.

References:

[Advertisement], Washington Post, March 28, 1974, p. E3. This advertisement for the Unitrex Mini Handy 80SR, offered as an alternative to the HP-35.

[Advertisement], Chicago Tribune, October 24, 1976, p. S10. Unitrex Scientific 21 sold by Zayre’s for $19.98.

[Advertisement], Biddeford-Saco Journal [Biddeford, Maine], October 16, 1976, p. 43. Scientific 21 on sale for $19.98.

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