datum

Something known or assumed as fact, and is made the basis of reasoning or inference which an intellectual system of any sort (such as knowledge or theoretical framework) is constructed.

a datum of experience

given this datum, it follows that

A point, line, plane, or surface with reference to which positions (such as elevations) are measured or indicated. (Examples include a permanent benchmark in leveling or mean sea level in a topographical survey).

A geodetic datum is sometimes also called a benchmark.

GD&T tells us that the center of a bolt circle is in fact defined by the locations of the holes themselves, as each is a datum.

A floating reference point, or SLDMB, used to evaluate surface currents in a body of water, and often employed by coastal search and rescue.

To provide missing data points by using a mathematical model to extrapolate values that are outside the range of a measuring device.

Removing the effects of any period of deformation by datuming or flattening selective reflection horizons should restore the structure prior to the datumed horizon, or the amount of deformation above the datumed horizon.

On the left the stacking velocity functions are datumed to sea level and show great disparity.