The most difficult clocks riddles

Both notations are correct and historically Roman numerals were often written less consistently than today. The notation 'IIII' is often seen on clock faces. The reason for that may be practical, to avoid confusing the IV and VI when the clock is held upside down (although other theories also exist).

A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. The first quartz clock was built in 1927 by Warren Marrison and J. W. Horton at Bell Telephone Laboratories. Since the 1980s, when the advent of solid-state digital electronics allowed them to be made compact and inexpensive, quartz timekeepers have become the world's most widely used timekeeping technology, used in most clocks and watches, as well as computers and other appliances that keep time.

Clock Safelight - this is element of photographic darkroom equipment used for precise adjustment of the lamp's operating time in the enlarger.

The Beverly Clock is a clock situated in the 3rd floor lift foyer of the Department of Physics at the University of Otago, Dunedin, New Zealand. The clock is still running despite never having been manually wound since its construction in 1864 by Arthur Beverly.

This is the clock from the time of the Great French Revolution. During this time the French replaced various non-standard units in physics with the decimal metric system. The 24-hour division of the day was also abolished in favour of 20-hour, however, this regulation did not survive.