Probably the only calc. supporting a stroboscopic display. Info from The first calculators: The essence of the display was represented by(with) a drum which is resulted in driving by the motor, spinned with frequency 1300 turnovers one minute. Inside the calculator the thyratrons are placed which flare during 100 us for ignition of the defined sign. In the same calculator the Reverse Polish Notation (RPN) for execution of calculations was applied. It means, that two numbers at first are entered, but only then the key with required operation is pushed.