http://mypeoplepc.com/members/jon8338/math/id8.html
This is also *part* of the math used for GPS. There are many other factors to consider.
transmitter stamp 12:00 at 12:01 receiver transmitter stamp 12:02 at 12:04 receiver
if c=speed of light,
distance = (12:04-12:01)c-(12:02-12:00)c=00:01c
Jon Giffen