Christiaan Huygens had shown in his 1673…

Christiaan Huygens had shown in his 1673 analysis of pendulums, Horologium Oscillatorium, that wide swings made the pendulum inaccurate, causing its period, and thus the rate of the clock, to vary with unavoidable variations in the driving force provided by the movement.

Clockmakers' realization that only pendulums with small swings of a few degrees are isochronous motivated the invention of the anchor escapement around 1670, which had reduced the pendulum's swing from 100° to 4°-6°.

In addition to increased accuracy, this had allowed the clock's case to accommodate longer, slower pendulums, which needed less power and caused less wear on the movement.

The seconds pendulum (also called the Royal pendulum) in which each swing takes one second, which is about one meter (39.1 in) long, become widely used.

The long narrow clocks built around these pendulums, first made by William Clement around 1680, become known as grandfather clocks.