Ref the commment in a previous post re the student not checking direction of spin before recovery. I remember this happening to me on a 30 hr check at Acklington in 63 - when the instructor banged the T&S the glass broke and the instrument flew apart, but I don't think I was also the student in a spin from 25k. Therefore this type of breakage must have happened more than once. Still it was difficult to carry out the check for direction when you had put it into the spin in the first place, and your left/right foot was extended in the direction of the spin. Eventually we (students) learnt to say the words but as an basic instructor today, I wonder how many students really look to see which way the aircraft is spinning before applying opposite rudder.