In the thirteenth century, mechanical clock was invented. this was more accurate, but was expensive to make. Over the next few centuries the design was developed. For example, springs were added around 1500.This improved accuracy and allowed clocks to be smaller. Mechanical clocks continued to develop until they had an accuracy of one-hundredth of a second per day.
In 1927, the first quartz clock was developed. A quartz clock is accurate because of the regular vibration that occurs when an electric current is run through the mineral quartz.
Solid Bulky
SRF Solid Recovered