If you want to mimic historical procedures, the main methods of getting speed were:
1. Ausdampfen: this is matching course and speed at a distance, on the surface. Can be done in game even without map contacts by carefully watching the target and adjusting own course and speed until a) the bearing no longer changes and b) the target appears to stay at the same range. To be accurate, best to do it over 30 minutes. 10 can suffice. It is most accurate at AOBs near 90, or near zero. As a sidenote, this is as you know very similar to how the US TDC was used to refine target data - adjusting the computer til bearing and range matched. The Germans just did it with their boat. Disadvantage here being no ability to refine the data once done with Ausdampfen.
2. Koppeln: this is plotting based on exact bearings and estimated ranges. The real guys were able to accurately estimate range based on how much mast was showing over the horizon and could use a Peildiopter (a pelorus) to get accurate true bearings. Also can be done in game with adequate practice estimating ranges by eye.
3. Schätzung: plain old seaman’s eye estimation, but also could include the “fixed wire” method of estimating speed by timing how long it takes for the target to transit the vertical line. They estimated length for this purpose based on an estimate of tonnage. The real guys (same as the Americans) did not rely on or have good rec manual data.
Any questions on the German TDC I’m happy to answer. Tvre.org is great but has some small errors here and there (he didn’t have all the documentation we now do when he sadly passed).
To answer your question about the position keeper, the German TDC at least from mid 1941 and forward, in other words the model S3, had a functionality called Lage laufend. That took advantage of the fact that every degree of bearing change equals 1° of AOB change. The computer also had direct connection to the gyrocompass and so, when told to do so, the computer would take own course changes into account as well as bearing changes such that if you kept the optics on target, the AOB would be correct regardless of own maneuvers. So you could call it AOB tracking is what it had. And then to minimize errors caused by parallax, they would strive for a zero or near zero gyro angle shot and then roughly input the range. SH games do not implement the gyrocompass connection and so own course changes will not be taken into account.
This writeup I did explains the mixture we have:
https://www.subsim.com/radioroom/sho...&postcount=209