JJ Sinclair wrote:

I'm not suggesting we fly around without an altitude readout of some
kind, but does it have to be the big, old 80mm round dial? Why can't I

No it hasn't to be 80mm, mine is 57mm. Aside from this, yes it has to:
More than once I was happy to be able to continue my flight under a
class C ceiling despite of two flat batteries.

Besides, many contries reqire gliders to be equipped with a certificated
altimeter.