I took some photos to help out someone on another (non shaving) forum, and thought that they might help out someone here too:
The photos aren't the best, as I didn't have a tripod handy, but they should give you an idea of the amount of blade angle difference that can be achieved with a Merkur 34c/HD.
1) Clearly, if you shave with the blade at this angle, you're going to be a long time waiting for that BBS you dreamed of:
2) Keep dreaming but notice the difference in angle of the razor handle:
3) Well, I guess if you have a beard an inch long, you might hack away at some of that hair, but you couldn't call it shaving:
4) Okay, if you went a week without a shave, you might now be trimming the tips of those hairs:
5) Now we're shaving! Notice how the angle of the blade is quite steep against the skin. This is sure to result in nicks or cuts if you apply too much pressure. Even if you don't cut yourself, you'll end up scraping the skin causing irritation:
6) The blade angle here is much shallower than in photo 5, which means only the very point of the blade edge is going to slice through the hairs and hopefully glide over the skin:
7) Now we're going too far the other way, just trimming the tips of the longest hairs:
8) We're not chopping trees you know:
The ideal angle will be somewhere between 6 and 7. Erring on the side of 7 will take more passes to achieve BBS but should give less irritation. Erring on the side of 5 will undoubtedly cause more irritation that necessary.
I hope it helps some folks out. If I've made any errors, please let me know...