the time of arrival of a constant speed moving object at a given location is calculated from data representing the time of arrival of the object at two preceeding locations and the relative physical distances between the three locations . an up - down counter counts up at a fixed frequency f 1 during the time interval of the object &# 39 ; s transversal of the distance between the first two locations and counts down at a pre - selected frequency f 2 thereafter . the preselected frequency f 2 is a function of the distances between locations and the fixed frequency f 1 . when the counter counts down to zero it produces an output pulse that occurs at the time the object reaches the given location . operation of the time delay computer is independent of object speed .