Another way is to get the position of enemy ship (if you dont know what type it is). Mark it, and start timer. Get second position 1 minute after. Measure distance, multiply with 60 (per hour), divide with 1000 (m to km) and divide with 1.85 (knots).
Example : ship travels 300 meter in 1 minute. (300/1000x60)/1.85 = 9.7 kn.
The longer time (and therefore distance) gives imho more precise reading as measurements are done in steps of 50 meters.
So a ship travelling 2 km in 10 minutes is travelling 2 x 6 /1.85 = 6.5 kn.
Tbh I usually dont use 1.85, but a rounded 2, and then adding a bit to the final result. That way its no 100% correct, but then again, I kinda like to sneak up really close, so a little on or off doesnt matter
