Texas Instruments Exactra 20 Handheld Electronic Calculator (TI-20)

This handheld electronic calculator is one of a series of “exactra” calculators introduced by Texas Instruments in the spring of 1974. It has an off-white plastic case, an orange keyboard, and eighteen nearly square plastic keys. These include ten digit keys, a clear entry key, a clear key, a decimal point key, four arithmetic function keys, and a constant key. An on/off switch and a $/F (for dollars / floating point) key are on the left in the top row of keys. A mark at the top of the keyboard reads: exactra 20. Behind this is a six-digit red LED display.

The calculator has no provision for a charger/adapter. A battery compartment at the top of the back would hold three AA alkaline or carbon-zinc batteries. A mark molded into the plastic on the back reads in part: TI-20 ELECTRONIC CALCULATOR (/) MADE BY TEXAS INSTRUMENTS INCORPORATED. It also gives instructions. Toward the bottom of the back is the stamp: 274. A tag below this reads: SERIAL NUMBER 2000036485.

Unscrewing two screws on the back allow one to remove it. The calculator has two chips. The larger one is marked: TMS 0135 NC (/) C7422. This is a TMS0135 chip. The smaller one is marked: M7419 (/) SN27882.

References:

[Advertisement], New York Times, May 2, 1974, p. 18. Exactra 20 selling for $39.99.

[Advertisement], Chicago Tribune, Dec 15, 1974, p. T17. Texas Instruments Exactra 20 selling for $19.88.

[Advertisement], New York Times, September 10, 1975, p. 6. Exactra 20 calculator, regularly $29.99, now $14.99.

Online Datamath Museum, accessed June 2, 2015.

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