Ground Level (GL) - The elevation above sea level.
Kelly Bushing Height (KB) -The height of the drilling floor
above the ground level. Many wellbore depth measurements
are taken from the Kelly bushing. The Kelly bushing
elevation is calculated by adding the ground level to the
Kelly bushing height.
Datum - A depth within a reservoir, measured from sea
evel and therefore is not dependent on ground level. This
gives a consistent or !level! plane within the reservoir to
refer to.
