For manual targeting I can recommend to check this post :
http://www.subsim.com/radioroom/showthread.php?t=88961
I use Manual Targeting as well however I leave Auto Map Contacts on to measure the distance. I really love to gather all the information including range manually however the stadimeter and the recognition manual are not handy in this subject.
Values in Recognition manual are generally false, even the highest mast in given picture does not match with highest mast value

Which makes stadimeter useless in my opinion. Did i miss something about it?
I know that in real life everything was not perfect including recognition manual. My nerves can take being depth charged for hours but I can't handle wasting Third Reich's precious torpedoes just because I wasn't qualified enough to calculate a range correctly.