Movement and measurement

If an object or event is in one position so that it can be measured at leisure, then time is not an explicit factor in its measurement. However, length units are defined in terms of time: “The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.” –NIST

Also, it takes time to make two measurements or to position both ends of an object next to a measuring rod and read the result. Measuring lengths by using signals traveling at the speed of light explicitly includes time and leads to the Lorentz contraction of relativity.

When it is movement itself that is being measured, the role of time is critical. The result is that we need to be careful about what it means to measure time.

Clocks are commonly used to measure time. This means that there is a movement external to whatever is under observation that is used as a standard of time. Is this necessary? No, it is entirely possible to calibrate a clock-like apparatus that is within the frame of reference, not independent of it. Moreover, it is misleading to use clocks as if time were an absolute in its own independent frame.

It is best to measure length and duration together. One way to do this is to have (or imagine) measuring wheels traveling along each axis (both positive and negative directions) to measure both lengths and times together. When a measuring wheel comes to an object or event in its direction, the value is recorded in units of length and time. Another method would be to use pulses of light.