 As well as addition , <unk> , <unk> and division , it had <unk> and square @-@ root functions , and the ability to <unk> by a fixed constant . With an eight @-@ digit display , the calculator could display positive numbers between 0 @.@ <unk> and 99 @,@ 999 @,@ 999 , and negative numbers between <unk> and <unk> . <unk> 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 leads 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 were used for memory operations . 
