1. In a key-operated program calculator adapted to achieve a specific program calculation in response to a plurality of kinds of input data items introduced sequentially thereto, comprising: an input data item display; means for exhibiting various and different types of symbols on said input data display during successive stages of a computation; said exhibiting means further comprising: means for displaying symbols on said input data item display which represent types of data inputs that must be entered for processing during subsequent computations; means for displaying different symbols on said input data display which represents types of data currently being entered for currently performing computations; and means for displaying other different symbols on said input data item display which represent the results of a previously performed computation.