It took me three attempts to get it right, putting the disassembled mech back in the bike doing test runs . The needle is a push fit it , goes back on fairly solidly. Putting the unit back together was a bit fiddly , as you can see the back of the silver glass retaining ring carries a few marks from its deformation. I now have an accurate speedo. Thanks to whoever it was that suggested moving the needle was the way to go, all those months ago. You were right!