Any tip for using the stadimeter?

[kstanb]

I am playing with RFB + RSRD + OM

and I am having a lot of trouble getting accurate ranges with the stadimeter, therefore my speed calculations and target course calculations done without radar or sonar assistance are always poor some of the issues:

- It is pretty much impossible to focus the tool while surfaced, the sub moves so much that it is even difficult to hit pause with the target centered.

- In the recognition manual I have 2 pictures for most merchant ships:
one is usually called, Medium split merchant, height 50ft. the other Medium split freighter 55ft. Or like Large tanker 60ft, Large oiler 52ft,
(I am inventing the numbers, but that is the idea)

- While submerged, sometimes, the target is so far away that it is impossible to "see" the contact at periscope depth. therefore, I have to surface and again try the very frustrating game of pausing with the target centered

So my questions are, does anyone have tips of how to improve range finding accuracy with using only the stadimeter?

thanks a lot