"grandfather"
by cm
Longcase Clock
Creative Commons Attribution Share AlikeLongcase Clock - Credit: boliyou, Flickr

Longcase, or “grandfather”, clocks were more accurate than contemporary equivalents because the longer pendulums had a slower beat (usually one per second) which caused less friction and required less power.   Such clocks only became technically possible with an innovation called the anchor escapement mechanism, around 1670.   Earlier pendulums swung to angles of up to 100º, which was too wide for a long pendulum to be accommodated within a case.   The new mechanism reduced that angle to 5º, easily fitting within the clock case.