Abstract: An instrument for determining and measuring the "X" and "Y" coordinate dinces a moving vehicle is located from a predetermined reference point at any given instant is disclosed as incorporating a tensioned range measuring wire, an angle sighting arm through which said tensioned range wire operates, range and angle potentiometers effectively connected to said tensioned range wire and angle sighting arm for constantly producing a pair of analog signals that are proportional to range and angular distances to said moving vehicle, respectively. A computer automatically computes the instantaneous "X" and "Y" coordinates of said vehicle with respect to the aforesaid predetermined known reference point from said pair of analog signals. An important and unique brake sub-combination permits the instrument and vehicle whose coordinates are being measured to be held in combined static equilibrium when they are not in use.