Various techniques for measuring time intervals are given below:

(i) Electrical oscillators: These use a.c supply of frequency 50 Hz, The rotations of a synchronous motor run on a.c. is used to obtain at scale.

(ii) Electronic oscillators: A vacuum tube or a semi- conductor device is used to produce electromagnetic oscillations of a very high frequency. The time period of such oscillations can be used to measure small time intervals.

(iii) Quartz crystal clocks: Quartz crystal shows piezo electric effect that is, if such a crystal is subjected to a fluectuating pressure across its one pair parallel forces, an oscillatory e.m.f is developed across another pair which is perpendicular to earlier pair of face and vice-versa.The oscillations so produced can be used to measure time intervals Such clocks are quite in use these days.

(iv) Atomic clocks: Such clocks make use of periodic vibrations taking place within the atoms like that of caesium.

(v) Decay of elementary particles : Many unstable elementary particles decay in very short time interval from 10^-10 second to 10^-24 second. By studying this decay, very small time intervals can be measured.

(vi) Redioactive dating: Very long intervals,Such as age of fossils (carbon dating), rocks and earth (uranium dating ) etc. are estimated by a technique known as radioactive dating.