Mini electronic calculator with blackboard display format

Claim 1

A mini electronic calculator for adding or subtracting two complete numbers comprising: A. an integrated circuit arithmetic unit having means to carry out addition and subtraction of two complete numbers entered therein; B. a keyboard associated with the input of the unit, said keyboard having three parallel sets of keys arranged along horizontal lines, the keys of the first set being constituted by a row of digit keys marked with the digits 0 to 9 for entering the first complete number, the keys of the second set being constituted by a corresponding row of digit keys for entering the second complete number, and the keys of the third set including a plus function key, a minus function key, an equal sign key and an erase key, said erase key being coupled to the unit to clear the display in preparation for a fresh computation; and C. an electro-optic display associated with the output of the unit, said display having three parallel groups of stations arranged along horizontal lines, the stations in the first group being digit stations for presenting the first complete number entered by successive actuation of keys in the first set, the stations in the second group being constituted by a lead station for presenting the function entered by actuating the plus or minus key, followed by digit stations for presenting the second complete number entered by successive actuation of keys in the second set, the third group being constituted by digit stations for presenting the result, whereby the display exhibits the first and second complete numbers and the result of a computation in a blackboard format, said first and second display groups each having three digit stations at corresponding locations to limit the complete numbers to three digits, the third group having four digit stations to provide the result, said arithmetic unit including means to disregard entries after three digits have been successively entered in the first group of digit stations and to disregard entries after three digits have been successively entered in the second group of digit stations.