Note: These formulas have been transcribed from EPSG Guidance Note #7-2. Users are encouraged to use that document rather than the text which follows as reference because limitations in the transcription will be avoided.¶¶A vertical offset allows calculation of coordinates in the target vertical coordinate reference system by adding a correction parameter A to the coordinate values of the point in the source system:¶X2 = X1 + A1>2¶where¶X2 = value in the forward target vertical coordinate reference system.¶X1 = value in the forward source vertical coordinate reference system.¶A1>2 is the offset to be applied for the transformation from CRS 1 to CRS 2. Its value for the forward calculation is the value of the origin of the source CRS 1 in the target CRS 2.¶¶For the reverse transformation from CRS 2 to CRS 1 the same formula is used but with the sign of the offset A1>2 reversed:¶	X1 = X2 + (–A1>2)¶¶Change of axis direction¶The above formulas apply only when the positive direction of the axis of each CRS is the same. If there is a requirement to transform heights in the source CRS to depths in the target CRS or to transform depths in the source CRS to heights in the target CRS, the formulas must be modified to:¶for the forward transformation:       X2 = mX1 + A1>2¶for the reverse transformation:        X1 = m[X2 + (–A1>2)]¶where m is a direction modifier,¶m = p1 * p2 ¶and¶	p1 indicates the positive direction of the CRS 1 axis; p1 = +1 if up, -1 if down;.¶	p2 indicates the positive direction of the CRS 2 axis; p2 = +1 if up, -1 if down¶These modified formulas remain valid whether or not there is a change in axis direction.¶¶Change of unit¶A further modification allows for source CRS axis, target CRS axis or offset to be in different units giving the general formulas:¶for the forward transformation:       X2 = {(p1 * p2) * (X1 * U1) + (A1>2 * UA)} / U2¶for the reverse transformation:        X1 = {(p1 * p2) * [(X2 * U2) + (–A1>2 * UA)]} / U1¶¶where U1 U2 and UA are unit conversion ratios for the two systems and the offset value respectively. U = [(factor b) / (factor c)] from the EPSG Dataset Unit of Measure table, populated with respect to the linear base unit, metre. U has a value of 0.3048 for the international foot.