TI SR-50

The SR-50 was Texas Instruments' first scientific pocket calculator with trigonometric and logarithm functions. It was an update of their SR-10 of 1973 which had featured scientific notation, squares, square root, and reciprocals, but no trig or log functions. The SR-50 was introduced in 1974 and sold for US$170. [ [http://www.thocp.net/hardware/ti_calculators.htm 20 Years of Texas Instruments Consumer Products] ] The SR-50 had a display with ten digits plus a two digit exponent for floating point numbers. It used ordinary infix notation, as opposed to the reverse polish notation employed by its rival, the Hewlett Packard HP-35. The SR-50 measured 5-3/4 inch long by 3-1/8 inch wide by 1-3/16 inch high (147 mm by 78 mm by 31 mm) and was powered by a rechargeable NiCad battery pack. It had 40 keys, an on/off switch and a degrees/radians switch. "SR" stood for "slide rule."

The SR-50 was followed by an updated model the SR-51. It had the same physical dimensions but added a 2nd function on most buttons. Most notable among the added functions were the ability to enter x:y pairs and do linear regression analysis on them. A further update resulted in the programmable model SR-52 in late 1975. It was twice as thick and could perform 224 program steps recorded on magnetic cards, similar to its competitor HP-65.

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