Normal gravity in the context of Earth's gravity

Dynamic height (symbol ${\displaystyle H^{\text{d}}}$ or ${\displaystyle H^{\text{dyn}}}$) is a way of specifying the vertical position of a point above a vertical datum; it is an alternative for orthometric height or normal height. It can be computed (in SI units of metre) by dividing the location's geopotential number (symbol C, in square metre per square second) by the normal gravity (symbol g_c, in metres per square second) at 45 degree latitude and zero height, a constant value (9.806199203 m/s):

Dynamic heights are usually chosen so that zero corresponds to the geoid.

Normal heights (symbol ${\displaystyle H^{*}}$ or ${\displaystyle H^{N}}$; SI unit metre, m) is a type of height above sea level introduced by the Soviet scientist Mikhail Molodenskii.The normal height of a point is defined as the quotient of a point's geopotential number C (i.e. its geopotential difference with that of sea level), by the vertically averaged normal gravity:

The average is evaluated along the normal potential's plumb line (a curve, approximated by the ellipsoidal normal, a straight line). The evaluation ranges from the Earth ellipsoid up to the point of interest; the procedure is thus recursive.Normal heights are slightly dependent upon the reference ellipsoid chosen.