Errors in the derived aspect, in course and speed of another vessel, or in the nearest approach, found by plotting radar ranges and bearings on a relative plot can arise in a number of ways, such as errors:

(1) in the bearing as read from the PPI

(2) in range as read from the PPI

(3) in plotting the points on the plotting sheet

(4) in estimating own vessel's course and distance run during the plotting interval

(5) in timing the plotting interval

(6) ‘blunders’.