Most people will tell you to do a plot with absolute bearings -i.e. plot starting from your sub icon on the map and keep the plot always from the sub's current position- but I found out long ago it is way easier to do it with relative bearings. Here's how to:
1.- Forget about starting from your sub, and go pick a place in the map where you can work and plot without distractions (An area of only water is ideal)
2.- Start by using vertical ruler to draw a line from bottom to top. This represents your sub's motion forward. Note your sub's speed.
3.- Now, scope up, get range and bearing to target. Start the chrono.
4.- From the initial point of the line you drawed in step 2) and using your ruler, draw a line in the bearing of the target. Use the compass in the tool helper to make it properly (Since the line you drawed is on course zero the compass in the tool helper matches exactly the scope bearing from your sub). Either use the compass in the tools or the ruler markings to make the line reach the proper measured target distance.
5.- 3 minutes later, up scope again and take bearing and range.
6.- First, calculate how much your sub has advanced in those 3 minutes with the easy mental rule. Now go that distance along the vertical line upwards and put a mark there. That's where your sub was when you took the second bearing
Now pick again the ruler and draw from there the bearing and range to target of your second reading.
7.- Repeat as necessary to get a good speed reading. Serves also to get angle on the bow easily, which you can measure with your angle tool. If you want target's true course, you must add substract that AOB from your true submarine course. That's all.
Advantages:
1.- Simple to use with the game tools
2.- No hurry to plot from where your submarine icon is each moment. You have three full minutes to plot your sub's and the target's new situation each time.
Hope that helps.
