As well as addition , subtraction , multiplication and division , it had reciprocal and square @-@ root functions , and the ability to multiply by a fixed constant . With an eight @-@ digit display , the calculator could display positive numbers between 0 @.@ 0000001 and 99 @,@ 999 @,@ 999 , and negative numbers between -0.000001 and -9,999,999 . Calculators of the time tended to have displays of between 3 and 12 digits , as reducing the number of digits was an effective way of reducing the cost of the calculator . A number outside that range lead to an overflow , and the screen flashes and all keys except the clear key are rendered inoperable to inform the user of the error . A independent memory register could read information from the screen , and information could only be taken from the memory onto the screen . Five keys was used for memory operations .