Friden EC132  USA  1964  
"This machine has the four
basic arithmetic functions: add, subtract, multiply and
divide. Squarerooting was an optional feature; compared
to the electromechanical calculators of the time this was
a major improvement, besides speed, quiet operation and
robustness. The Friden 132 calculator uses 'reversed
polish notation': 2+(3/8) is keyed in as 2 3 8 / +. This
principle, which obviates the use of parentheses, was
later followed in the wellknown pocket calculators of
HewlettPackard. The results of the computation are shown
on a small CRT screen. The machine is built from separate
transistors, memory is implemented using a
magnetostrictive delay line. The machine is a fine
example of careful industrial design." 

Source: Bob Lichty 