HP 9100B upgrade and case mod

I thought my latest little retrocomputing project might beof interest. A few weeks ago, our accounting department trashed some oldequipment that had been in a closet sine the 70?s. Because it was all fully depreciated long ago, the stuff wasup for grabs. Most of it was junk,but they did have 5 HP 9100B calculators that seemed to be in pretty goodphysical shape. These are from the1960?s, and are pretty huge for a calculator, by today?s standards. I tried them all, and they all seemedto have some pretty weird behavior. When you hit the ?+? key, it doesn?t wait for another number, butinstead adds the last row directly to the second row. I suppose that?s why these have been out of commission allthese years. View image: Strange calculator behavior