No Problem ddiplock.
So you have timed a ship and in 3 minutes it has travelled 0.4 nautical miles. To find the speed:
1. Simply draw a line, anchoring it on the 3 minute mark on the time scale.
2. Extend it so that it crosses through the 0.4 miles mark on the distance scale.
3. Finally extend the line so that it crosses the speed line, where that line crosses should indicate the calculated speed.
It might not give a round figure, for example, if the line crossed roughly half way between say 5 and 6 knots then put in down as 5.5 knots etc something like that.