Here is an article I have pulled from another website. I have used it to take apart speedometers and tachometers but prefer the simple method of cutting the band.
Start by prying open the retaining ring with a utility knife, from the bottom side. Pry the ring up just enough to fit in a small common screwdriver.
Be careful with the utility knife..they're very sharp.
Pry the retaining ring upward as you work your way around, opening only about a 1/16th inch gap. Don't twist the screwdriver, it'll just make a mess of the ring. Only push the handle downward, prying upward a very small section (1/4 to 3/8s inch at a time) of the ring. It does take a while to get all the way around, so be patient.
Remove the screws in the back.
Start by prying open the retaining ring with a utility knife, from the bottom side. Pry the ring up just enough to fit in a small common screwdriver.
Be careful with the utility knife..they're very sharp.

Pry the retaining ring upward as you work your way around, opening only about a 1/16th inch gap. Don't twist the screwdriver, it'll just make a mess of the ring. Only push the handle downward, prying upward a very small section (1/4 to 3/8s inch at a time) of the ring. It does take a while to get all the way around, so be patient.


Remove the screws in the back.
