: Thanks Graham. I believe that has been done, I presume that the
: tachy ring can't be removed without the glass being removed.

: Stewart

Okay, going on another stage.....
With the movement taken out, support the case on a piece of aluminium tube, slightly larger than the bezel diameter, so the edge of the tube "seats" on the radius of the case.
Then, measure the inside diameter of the Tachy ring.
Take another piece of tube, with an OD slightly smaller than the ID of the tachy, and pass it through the case until it contacts the glass.
Then press the smaller tube to press the glass out of the case.
This way you are pushing the whole diameter, square, and should not damage the tachy ring.

Does that make sense??