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Programmable calculatorsTexas Instruments SR-22
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Datasheet Years of production: · Display type: 7-segment
New price: · Display color: Orange
· · Display technology: PFD
Size: 9½"×6½"×2½" Display size: 10+2 digits
Weight: 3 lbs · ·
· · Entry method: Algebraic
Batteries: 4*×"D" internal NiCd Advanced functions: Floating point base-N
External power: TI adapter Memory functions: N/A
I/O: N/A · ·
· · Programming model: N/A
Precision: 12 digits Program functions: N/A
Memories: N/A Program display: N/A
Program steps: N/A Program editing: N/A

sr22.jpg (80330 bytes)If you look closely, you might just be able to discern a strange number on this calculator's display: 3.243F6A888. No, it's not a faulty device. Yes, that is the value of pi. How come, you ask? Well, the SR-22 is a very unique device: possibly the world's only electronic calculator that is designed to do integer and floating point arithmetic in three number bases, decimal, octal, and hexadecimal.

This absolutely unique device was part of Texas Instrument's first series of calculator offerings. Although not a programmable machine, it is definitely a programmer's tool, and thus it has a place in this collection. Even if its beautiful Panaplex display didn't warrant it, how could I possibly resist a calculator that can be used to compute the factorial of AAhex and correctly display the result: A.55bC32206expFE?

And in case you wanted to know (I did), the value of e in hexadecimal is 2.B7E1516280C. Computing it (or indeed, the exponential of any number) is easy even on a four-banger. The formula to use is this:

ex=x0/0!+x1/1!+x2/2!+...

This series converges quickly, and on an algebraic calculator with no precedence logic, it can be computed very easily. On the SR-22, once you put x into memory using STO, you can then proceed with the following keystrokes:

RCL ÷ 7 + RCL ÷ 6 + RCL ÷ 5 + RCL ÷ 4 +
RCL ÷ 3 + RCL ÷ 2 + RCL ÷ 1 + RCL =

Of course for greater accuracy, you can start with a number greater than 7; to compute e to 10+ hexadecimal digits, I started with Fhex.