Dr. Steve Rapp, 2005

The Datum

A Datum is a reference point used
when making a measurement (in this case, it is the ground).
Suppose we
wish to find the difference in height between the third
floor and fifth floor of a building. H= h5 – h3 = 50 ft.-30 ft. = 20 feet

30 ft.

50 ft.

The only requirement is that the datum not change in the middle of
the
calculation.

Ground