TI SR-50

The SR-50 was Texas Instruments' first scientific pocket calculator with trigonometric and logarithm functions. It was introduced in 1974, sold for $170, and 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" reportedly stood for "slide rule."