A time measuring system defined to relate the passage of temporal events since a selected epoch. Note: The internationally recognized time interval is the second. Time scales are graduated in intervals such as seconds, minutes, hours, days, and years, and in fractions of a second, such as milliseconds, nanoseconds, and picoseconds. 2. Time coordinates placed on the abscissa (x-axis) of Cartesian-coordinate graphs used for depicting waveforms and similar phenomena.