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Programmable calculatorsTexas Instruments SR-50
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Datasheet Years of production: · Display type: 7-segment
New price: · Display color: Red
· · Display technology: LED
Size: 3"×6"×1½" Display size: 10+2 digits
Weight: 9 oz · ·
· · Entry method: Algebraic with precedence
Batteries: BP-1 (3×"AA" sealed NiCd) Advanced functions: trg, hyp, exp, log, drg, dms, stat
External power: TI AC-9130 adapter (8.2V AC 225mA) Memory functions: +/-/×/÷
I/O: N/A · ·
· · Programming model: N/A
Precision: 12 digits Program functions: N/A
Memories: 1 Program display: N/A
Program steps: N/A Program editing: N/A

sr50.jpg (21992 bytes)The SR-50 was Texas Instrument's first full-featured scientific calculator. It was the company's response to the challenge presented by the Hewlett Packard 35.

The SR-50 is a sleek, very well designed scientific calculator with a large, 10+2 digit display. Unlike later Texas Instruments models of similar appearance that felt like a creaky box of cheap plastic, the SR-50 has a solid, instrument-quality feel.

Despite its historic significance, the SR-50 would normally fall outside my main area of interest, programmable calculators. However, once again I was unable to resist when I was presented with the opportunity to obtain a specimen in excellent condition (as the image on the right shows, the silver trim is entirely intact, which is quite a rarity) at a bargain price.

There is also another reason: the SR-50 belongs to a family of four calculators that are closely related to the first line of programmable calculators (including the SR-52 and SR-56) from Texas Instruments. Of these, the SR-50 and SR-51 have an almost identical appearance; the same is true for the SR-50A and the SR-51A. However, it is the SR-51 and SR-51A that have a connector in the battery compartment which can be used with the PC-100 printer cradle, when the printer is switched to SR-52 compatibility mode. I don't have any documentation with my SR-51 or SR-51A (I received the SR-51 as a gift, and obtained my SR-51A by chance, advertised as non-working, along with an SR-52) but the lack of any printer-related keys on its keyboard appear to suggest that printer compatibility might not have been officially supported. It also makes one wonder: are there any other functions this calculator may have that aren't accessible from its keyboard? If only I knew the specifications for the bidirectional PC-100 printer interface...

The SR-51A was also the first calculator I ever saw that had a built-in random number generator. One also gets the feeling that its conversion functions (2nd followed by a two-digit number) are in fact implemented as ROM-based programs that are not unlike the keystroke programs on programmable models.

Incidentally, the SR-51 had two other variants, however, these more properly belong to the next generation of Texas Instruments scientific calculators, with a much cheaper construction. The SR-51-II is a non-programmable scientific calculator, but the TI-51-III is actually identical to the TI-55, with minimal programmability.