The time, its calculating and storage.
What is the notion time? It is a difficult question. Generally speaking, it is an order of changing events, an order of constantly changing conditions of solids, Universe - being. The time is continuing being, living world.
The time meaurement is based on the observations or fulfilment of periodically repeated processes of the same duration: so for the measurement of the great intervals of time we use a year. The day rotation of the Earth relatively the stars determine the star time. In practice people use the solar time. The time, determined for the given longitude, is called the local time. The local average solar time of Greenwich meridian is called the world time. For practical convenience there is a system of zone time in the most countries. The time of the 2-nd zone time in Russia is called moscow in many states. On the summer period in many states all watches are put on 1 hour forward (i.e. summer time). A uniform system of time counting - ephemeris time is tested by observations of the Moon turning around the Earth. Fully independent from astronomic observation uniform system of the time counting is based on the concept of atomic second (see quantum watches). The time measurement and keeping is fulfilled by different watches and clocks.