Hewlett-Packard HP-33E electronic programmable scientific calculator complete with mains transformer (c.1979).
The HP-33E was one of the basic scientific programmable members of the HP30 series. The 33E model had conventional memory which lost its contents when power was turned off. (After this series, continuous memory was considered basic functionality. Data loss was normal for older calculators when the power was turned off.) The calculator had two shift keys in order to make room for the programming keys. Some preprogrammed features had to be omitted including hyperbolics, percent change and most unit conversions. Also, because memory space was needed for programming, storage registers were limited to 8. In place of these features and storage registers they provided 49 step programming similar in style to other calculators but at less cost. The HP-33E/C also included linear regression and estimate, %, and degrees/radians conversion – functions not available on some other models.