Ever since I got ahold of Silent 3ditor;
http://www.subsim.com/radioroom/down...o=file&id=4489
I've been modding and tweaking the game to suit me, so the periscopes, TBT, and binoculars are all changed so they do 3 different ranges. Couldn't tell you exactly how since it's been a long time since I made a lot of these tweaks.
As for real life, yeah, the hash marks were used to estimate range and lead angles - again, using the training wheels, take screenshots and get an idea of how many "divisions" in high and low power different ships fill at different ranges. Do that long enough and you'll have a fair idea of approximate range at first glance. Like the old joke about how do you get to Carnegie Hall...