The discipline imposed by these public clocks still remained lax by contemporary standards. A clock that only strikes the hours can only record the nearest hour that has passed; most early clocks had only hour hands in any case. Minute hands did not come into widespread use until the pendulum enabled a large leap in the accuracy of clocks; for watches, a similar leap in accuracy was not made possible before the invention of the balance spring. Before these improvements, the equation of time, the difference between apparent and mean solar time, was not even noticed.