On a latitudinal line, the departure of the closing distances is
distributed among the courses in proportion to the total record
departure for each course.
So to distribute the departure of the closing error in this problem,
the proportionate ratio is the same as single-proportion.
The departure of the closing error is to the sum of the record
departures as the adjustment to each departure is to the accumulated
record departure of each course or D1 is to D as A1 is to A or B1
is to B in our sample drawing.