Friden Model 132 Calculator, 1965. wikipedia 
The Friden 130 had a 13-digit capacity and a 5-inch CRT display. It was the first calculator to use reverse Polish notation (RPN), which eliminated the need for parentheses to specify the order of operations in complex calculations. The successor model EC-132 added a square root function.
The Friden wasn't programmable but its simultainous display of multiple registers made each keystroke seem powerful. I can remember drumming series calculations on the keyboard. For example, the square root, repeatedly applied to any number, converges on 1.0.
See also HP-35