Confusing passage in U-boat commander's handbook

[Hitman]

Ha ha good job , you found one of the translation errors I have noticed so far in the english version of the UKH

The fixed line this refers to, is NOT the horizon, but the fixed line or wire in the periscope, which you can use to measure speed exactly as the U-Jagd tools reflects. In the original german version there is no "(of the horizon)", as this is something that the translator added himself, probably to try to explain what he understood, but which is utterly WRONG. I was also puzzled with that until I could get the german version, and knew about the fixed wire speed measuing method

The scond paragraph is also wronly translated. First, it is NOT "masts at a given height", but masts OF KNOWN heigth.

Second, it is NOT a "1/16 scale", but a 1/10 scale, and it refers to the vertical scale in the periscope. Here's how it works:

The procedure is to be used mainly as close to 0º AOB as possible, i.e. when you have submerged forward of the target's course and it is coming at you (Not coincidentally, the main procedure the UKH suggests to approach an escorted convoy).

1.- Estimate the enemy mast heigth. Let's say it is 25 metres. Measure the mark of the scale it currently reaches. Let's say it is the "5" mark. Start the chronometer.

2.- Make frequent short observations until the mast covers double as many marks in the scope as in the first observation. In this case, when the mast reaches the "10" mark you are ready. Stop the chronometer and read the time it took for the mast to double its observed size. In our example it took let's say 1 minute.

Use the following formula:

((Mast in metres x 10) / Time in minutes ) x 0,03 = Enemy speed in knots.

Now, using that formula in our example:

((25 metres x 10) / 1 minute ) x 0,03 = 7,5 knots.

You must now apply as a correction your own U-Boat speed. If you were going towards the enemy at 2 knots, then substract that from the 7,5 knots. So, 5,5 is the true enemy speed.