latest HP-01 battery replacement experience

[brouhaha]

I just replaced the batteries in my HP-01 again. Once again, the case back was screwed on too tight to remove it with just the Armstrong Metalcraft HP-01 battery tool, despite that when I last replaceed the batteries, I used that tool to tighten it, to only finger-tight.

When I first got the HP-01 in the 1990s, I didn't have any suitable tool to open it. I bought a generic jeweler's watch case tool for (IIRC) about $60, It came with a few different bits, and was provided in a wooden case. Unfortunately at some point I misplaced the tool. The next time I needed it, I found one online for about $30, without the wooden case.

Years later I got the Armstrong HP-01 tool which I very highly recommend.

However, now the case back was somehow too tight to easily open with that. I looked for my jeweler's case openers, and now couldn't find either one. I did another online search, and found that Harbor Freight now sells them for $7. I'm not a huge fan of Harbor Freight, as their quality is quite variable, but in this case the $7 tool, puchased for $4.89 after a discount, was adequate to the task.

The jeweler's case tool has a handle which makes it easy to apply a little more torque than one can by hand with the Armstrong tool. It didn't take much effort with that to loosen up the case back, and then I used the Armstrong tool to finish opening it, and to close it again after replacing the batteries.

If you use a jeweler's case opener, be careful to apply NO downward force into to the slots in the HP-01 case back, as it is possible to damage the pizeo buzzer used for the alarm. Only apply counterclockwise rotational force.

Armstrong Metalcrafts also makes a lot of other cool stuff, like orreryies, Napier's Bones, and Genaille Lucas Calculating Rulers.