> the buttons on the 11C and 15C were awesome

What is the trick to engineering HP calculator keys? Nobody gets keys right like the old HP calculators.

In this age of 3D printing and fast prototypes, we really ought to be able to crack this.

I was part of a group touring HP labs in the mid-1970s.

They showed us how they computed the key dimensions and typography with an (HP) minicomputer, then had it print out the commands for some kind of numerically controlled cutting machine on paper tapes using an old ASR33 teletype.

The cutting machine generated moulds for the injection moulding machines making the keys.

The keys are in two parts: light coloured digits and symbols and darker plastic forming the shape of the key itself and surrounding the lighter symbol plastic. As a result, they can be worn down but they can never wear out.