Horology refers to the science or study of measuring time. It also refers to the art of designing instruments for measuring time. Clocks, watches, time pieces, sundials, hourglasses, timers, atomic clocks etc. are various types of instruments for measuring time. Antique horology products include clocks and pocket watches from 17th century, Mechanical music and Singing birds from 18th century and wrist watches from 19th century.