in artillery, an auxiliary point by which artillery guns are registered with a view to a subsequent transfer of fire to destroy a target.
A distinction is made between an actual datum mark, which is an adjustment target or observable terrain object whose coordinates are known, and an imaginary datum mark, which is the center of a group of explosions whose coordinates are determined by intersections from the points of combined observation or optical reconnaissance. Imaginary datum marks include sound ranging check points based on the intersections of sound ranging stations and check points in high-burst registration with time fire.
Adjustment by datum marks is used where targets are not observable or where it is undesirable to make adjustment against the target itself, for example, to gain the element of surprise in a strike.