Most calculators clear the display after each calculation, erasing previous entries. However, it would be incredibly useful to maintain a record of past calculations and easily recall them.  This functionality can be effectively implemented within an Android app. Here's how it would work.

Below is a simple calculation. 1st answer is 6912 in [] as the answer. -7148 is next answer in []. There a 2 numbers starting with 5. (5678, 5421). By typing 5, all numbers starting with 5 are shown in the pick up window. By clicking any number, the number is auto typed.