DETERMINATION OF THE CONTACT'S TRUE COURSE AND SPEED
(1) Parallel own course line (OC) to the contact's first position (m1) and draw a line (called a vector) in the same direction as own ship's course line, with the head of the vector pointing towards (ml). Place an arrowhead on this vector and label this (r).
(2) Determine the length of own ship's true vector. Use own ship's speed and the time interval between the first and last position of the contact to enter the logarithmic scale to determine own ship's distance run in that time period. Lay off this distance along own ship's true vector line, mark the distance run and label this position as (e). The direction of this vector is from (e) towards (r) and will always have the same direction as own ship's true course line (OC).
NOTE: Two sides of the vector triangle have now been formed.
Side #1: Relative Motion between the first and last position's of the contact.
Side #2: Own ship's true course and distance run vector from (e) towards (r).
The remaining side of the triangle is the contact's true course and speed vector.
(3) Label the last position of the contact point (m). Connect point (e) to point (m). Terminate this line (vector) with an arrowhead pointing towards (m). Parallel the line from (e) to (m) to the center of the plotting sheet and read the true course to the contact from the compass rose, using the arrowhead to prevent choosing the reciprocal of the correct course. Measure the distance from (e) to (m) and enter the logarithmic scale with this distance and the time run between the contact's first and last positions to obtain the contact's speed.
NOTE: ALWAYS REMEMBER NO MATTER WHAT SHAPE THE VECTOR PLOT MAY TAKE, IT ALWAYS HAS THREE (3) SIDES YOURS, HIS AND THE RELATIVE MOTION.
