Horology (via Latin horologium from Greek ὡρολόγιον, from ὥρα hṓra "hour; time" and -o- interfix and suffix -logy; lit. "the study of time") is the art or science of measuring time. Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time.