How can gyroscopes be used to find the angular velocity?

[Physgeek64]

I was reading that gyroscopes can be used to measure the angular velocity of precession, such as in the Hubble space telescope, but mathematically how can this be done?
Many thanks

 

[mfb]

You measure the torque required to keep the gyroscope in its orientation relative to the spacecraft .
Wikipedia has an article about it.