DETERMINATION OF THE RELATIVE SPEED
Measure the distance along the RML between the first and last positions of the contact. Be sure to detennine this distance on the same scale used to plot r, m1, m2, etc. Enter the logarithmic scale with this distance and the elapsed time between the first and last position of the contact to obtain the relative speed of the contact along the Relative Motion Line.
DETERMINATION OF THE TIME OF THE CLOSEST POINT OF APPROACH
Measure the distance from the last position of the contact to the CPA. Enter the logarithmic scale with this distance and the relative speed, to determine the additional time required for the contact to advance from its last position to the CPA. Add this time interval to the time of the contact's last position to obtain the time of CPA.
A second and simpler method is to use your dividers measure the distance between r and m1 and walk this distance down the RML line to the point of CPA. As an example, lets say you measure between r and m1 (6 minutes of travel) and walk it down the RML line to CPA in 5.5 measures. You would then estimate that CPA would be in 33 additional minutes.
