Aren’t there eight line judges in tennis? Does the machine need a minder?
I think just 7.
Two at each end (4)
One on the service end sideline at the baseline (1)
Two on the receiving serve sidelines, one at the baseline and one at the service line. (2)
Does that make sense?
I guess you could permanently place one at each service line, vs. switching back and forth between serves, for an eighth.