Comparing button pressure between various HP calculators & DM15L

[Dave Britten]

I've taken a very similar approach using my wife's digital-scale measuring cup with a calculator laying over the top. That one has reasonably fast updates to the read-out, but not so fast that I couldn't read the numbers.

And I've observed results similar to yours: SM calcs tend to require quite a bit more force than HPs, and the force from key to key is much less consistent.