Satellite navigation

Everything in satellite navigation comes back to clocks, so it is worth knowing how German says that a clock is wrong. English says a clock is fast or slow; German says it goes ahead or goes behind: die Uhr geht vor, die Uhr geht nach. The verb is gehen throughout, die Uhr geht richtig is the one that keeps time, and die Uhr geht nicht does not mean it is slow but that it has stopped. From the same verb comes der Gang, the rate at which a clock gains or loses, and with it the compound in this list, der Uhrengang. Keep it apart from der Uhrenfehler: the error is how far a clock is off at this moment, the rate is how quickly that error grows. The quartz clock in a receiver has plenty of both, which is why nobody corrects it in advance. Its error is estimated afresh with every position, mitgeschätzt, as one more unknown.