The value H ^H_N found for the elevation of a point P _N by dividing the geopotential number W _N by an approximation g ^H_N to the average value of the acceleration of gravity along the vertical between P _N and the geoid: H _HN = W _N / g ^H_N. W_N is calculated from the measured differences ΔH _n of elevation between points P _n-1 and P _n along a route from point P _o on the geoid to P _N, and the measured or otherwise determined values gn of the accel-eration of gravity at these points P _n: W _N = Σ g _n ΔH _n (n = 1 to N). The value g ^H_N is calculated from the measured value g _N of the acceleration at P _N, the Bouguer gravity correction δg _B, and the free air gravity correction δg _f: g ^H_N = g _N - δg _B - δg _f / 2. This is approximately the value of the acceleration at a point on the vertical through P _N and halfway between P _N and the geoid. The Helmert elevation is also called the Helmert height.