Texas Instruments SR-51 (early model)

With the SR-51 Texas Instruments started a series of scientific calculators that added statistical functions and conversions to the "usual functions". You'll find similar performance and keyboard layout in the line SR-51 -> SR-51A -> SR-51-II -> TI-55 -> TI-55-II -> TI-55-III. But none of them was done as perfect as the SR-51. It was designed to stay decades as the close relative SR-50. Compared to the previous models the SR-51 got a keyboard design with white, grey, yellow and orange keys and gave an outlook to later TI calculators.

To reduce manufacturing costs and to give a similar appearence to the SR-52 and SR-56 calculators the SR-51 was replaced within a few months with the SR-51A. Logically it's quite rare. 

Nevertheless there are two different variants known: 
This model from an early production lot uses huge yellow characters for the shifted 2^nd-functions while later SR-51 sports a much finer printing. (Kirk B. Muri provided the picture on the right. Thanks!)

Fellow collector Gary Snyder reported in September 2010 that on the earlier versions the cancel exponent entry label (above the [EE] key) has an overbar over the EE text. On the later models the label has a slanted line striking through the text.

The SR-51 was introduced in January 1975, nevertheless the firmware of the calculator was released already three month earlier. Please notice the Date code 7442 printed on the TMC0523 SCOM (scanning read only memory) chip storing part of the program of the calculator.

Interesting to know, this calculator works with the PC-100 "Printer Craddle" developed for the SR-52 and SR-56.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, July 14, 2002. No reprints without written permission.