well, I've got three bikes with Avocet speedometers, and one or two more in the parts box. I've got a few pdf'ed manuals that I pulled off of the web (which might still be out there). Here's my quick summary:

Avocet 30: current speed, max speed, timer, clock, trip distance, total distance. Only one thing can be displayed at a time. The manual is for the Avocet 30 and 31. It doesn't mention how the 31 differs from the model 30.

Avocet 35: current speed, max speed, average speed, trip distance, total distance, timer, and clock. It does have a sleep mode, so it might burn a little less power than earlier models. I still have to replace the battery every year, though. Only one thing is displayed at a time.

Avocet 45: this has a two line display!!! I like this because it shows me the speed and distance, which are the only things I care about.
Functions:current speed, max speed, average speed, trip distance, total distance, timer, and clock. It has provisions for a cadence pickup, which adds the cadence function and "gear inches" function. There is also a "destination time" function. I can't imagine actually using something like that.

Avocet 50: this was the really cool one that could measure cumulative feet of climbing. They tended to have a short lifespan, so the odds of finding a functioning one is pretty slim. I don't recall what else it did.

That's all I know about. Let me know if you need a copy of these manuals.

Steve in Peoria