Recently, I was looking for the rectangular/polar conversion keys on my HP-49G+, only to find that they don't exist. That made me think about what the base level features of a scientific calculator should be. Looking back through older HP models, ->R and ->P seem to be present on just about every basic scientific calculator made after the HP-35, even on the bare-bones HP-21. ->RAD, ->DEG, ->H, and ->H.MS are also available on most models. These features are also available on TI's bottom of the line scientific calculator, the TI-30Xa.
What functions should be in the basic set of operations, either on the keyboard or easily available through menus?