HP and DM key Pressure

[RPZ]

Hello All,

I recently had my interest in HP calculators renewed and
found this group. Thank you for this wealth of knowledge.

Besides HP calculators I also have acquired a DM42 and
a DM41X beta. Marvelous machines.

As others have noticed, the keys seem a bit stiff.
By how much?

I decided to make some measurements using a test tube and
lead shot to measure the pressure required. Quite tedious
and hard to place the bottom of the tube in the middle of the key.
Also spilled the tube once. Real mess on my tile floor.

It occurred to me that I have an old spring and dial scale
that might work. I placed the calculator on the scale and
pressed the key just as I would in use and then subtracted
the calculator weight. I only did the number keys.
Not very sophisticated but this method seems quite repeatable
and appeared to be accurate to + or - 1/2 ounce.


Calculator Key Activation Pressure, RPZ, 09-21-2020


Model ------- Condition --- Range in Ounces


HP 41CX ----- well used ------- 4 - 4

HP 25 -------- well used ------- 5 - 6

HP 12C ------- well used ------- 5 - 7

HP 35 -------- well used -------- 6 - 7

DM42 -------- almost new ----- 7 - 11

DM41X ------- almost new ----- 9 - 12



Some folks have mentioned that with use the keys break in.
These measurements will allow me to retest later and see
if that is true or if it is just in my head.

Regards, Rick



---eof