ADC Ridge

I wanted a totally foolproof altimeter, so this single-function, totally-mechanical design was appealing. It's a bit bulky compared to many digital models, and the tiny marks on the dial are a bit hard to read correctly especially when I'm sleepy from an alpine start, but on the other hand it's fairly cheap - REI lists it online for $60 but I found mine in the store for $40.

The only problem is, it won't stay calibrated. You calibrate it by rotating a bezel on the outside of the dial - dirt simple. The problem is that there's no way to lock the bezel in place after calibration. So the next time anything bumps against the altimeter, say goodbye to your calibration. After calibrating to 8,350 ft on the summit of Mt St Helens, followed by a couple of glissades, this altimeter showed an elevation of 14,000 ft at treeline.
It makes no difference whether you keep the altimeter in a pocket or on a sling outside your pack or over your shoulder, there's no way to sufficiently protect the bezel short of building a custom case.

Normally, a wildly unreliable altimeter is a dangerous object, but this one shows its stripes so quickly that I can't imagine anyone would actually rely on it.

I'm happy to report that REI took my return with no fuss, so I still have $40 toward the price of my next altimeter.