@kenshirriff that doesn't look the gas gyros my dad worked on (he worked on guidance systems all his life, mostly on things we'd rather not see used). The gas gyros I saw -- which may have been from an accelerometer, instead of being a guidance gyro -- were cylindrical. The only spherical gyro I saw was an electrostatic gyro. Yes, that is beryllium, yes, I washed my hand afterwards. It is hollow, weighs 9 grams, and if you spin it at 36,000rpm on the proper axis, very, very spherical.