Thanks hitman.
The slide rule has as many functions as there are mathematical problems related to trigonometry, but I will stick to one examlpe here. Once you have fully internalised this procedure, other uses will just spontaneously leap out at you.
This procedure is to solve the Speed Problem.
The outer ring we will call Peilung
The middle ring we will call Strecke. The outer and inner circles of this wheel give distances in meters. The middle circle gives speed in knots.
and the inner ring we will call Zeit
To obtain a speed solution once you have obtained an AOB estimate (really it need not be a perfect estimate), set yourself up on an intercept course and start the stopwatch. Do not then change course or speed until the procedure is over.
Note the target AOB and the current periscope angle to target.
Find the point on the peilung ring which corresponds to the observed AOB of the target. Turn the strecke ring until your current (and constant ) speed is directly under the target AOB on the sliderule. Now look at the point on the Peilung that corresponds to the observed periscope angle (bearing) to target. Under this, on the strecke ring you will observe a different speed. This is the target speed assuming you bearing to target remains constant. i.e. you are on a collision course.
E.g. 1. Let's say you have an intercept course. The target is directly on your beam (i.e. bearing 270 = 090 on the peilung) observed AOB is starb'd 35, your speed is 4 knts
Match 4 knts to 35 on the peilung wheel,then look under 90 degrees and find a target speed of 7knts. If the bearing to the target is constant after 3-5 mins, then you are on a collision course and your target's speed is in fact 7knts.
However, let's say you pop your periscope up in 5 minutes exactly and in fact the target is now at 280 (80 on the peilung wheel).
Now you need to take a range measurement. (Let's say 1500m)
You set the measured range to target against the ORIGINAL AOB., So that's 1500m to 35 on the peilung rad.
Now you set the time interval (5 mins) on the Zeit wheel against the difference in bearing to target on the peilung rad. The difference in bearing to target is in this case 280-270=10 degrees.
The pointer on the Zeit wheel is now pointing to a speed of 3 knts. This is the speed correction. Becasue the target moved forward relative to you, you add this speed correction to the orginal speed estimate. That is 7knts +3 Knts = 10knts
Had you moved forward relative to the target, then you would have to subtract this speed correction.
That's it.