[NefariousKoel]

RedHammer...

If you're using the 3 minute (3:15 for metric) rule, use the map tools. As I said before, I keep "show on map" difficulty since the Stadimeter is screwed for me.

Anyway, in this case - take the pencil. Zoom in on the ship you're targeting until you can see it's shap instead of a symbol. Bring up the stop watch, which is accessible by left-clicking once on the periscope tab, then L-cliking on the stopwatch symbol. Now take your pencil and make a mark right in the center of the target ship and smartly right click to get rid of the pencil and click the stopwatch to get it started.

A bit before 3 minutes have passed (I prefer Imperial), zoom in on the map around your target, take the pencil again, and make another mark right in the middle of it when the timer hits 3. Leave the stopwatch going in case you can get a 6 minute in for double-checking.

Now, click on the Ruler. With the ruler tool ready, click on your first pencil mark, then aim for your second one (the 3 minute mark). Multiply that amount by 2 and drop any decimal points. That is it's speed in knots. Ex. - 0.6 nm = 12 knots.

Note: I generally check exactly how far the bar is (in this example) from 0.5 to 0.6nm. If I see that my second mark just barely makes it to 0.6nm but not in the middle of that range on the ruler (ex.), I subtract 1 knot off the end result.

If you manage a 6 minute test, it will run true every time. Just drop the decimal point on range and that's the speed in knots after 6 minutes.