Your method(s) would work for me too, as long as I stayed consistent from setup to setup, and realized other folks might use a slightly different set of selections to get their own measurements - which thus might be slightly different, and yet consistent for them from setup to setup also.
To me these photos are good examples of some of the difficulties in measuring these, and how much subjective judgement or selection actually enters in. In the photos, the bottom of both the toe and heel/top of binding look sloped, not flat, relative to the plane of the ski. With the toe, I'd have probably chosen the center of the sliding plate the boot rests on, rather than the spot you chose. At any rate, in such cases, I mostly would have to pick a point that seems to be close to the center of the weight at the toe or heel (or use some other consistent criteria), as you seem to have done. (If that is not the case here, then it certainly is with many bindings I've measured: one has to use one's judgement about where to place the calipers/rule.)
Also, the actual boot/binding contact points are possibly hidden, in the crevice, in the dark - in the photos (or in real life), one simply can't see in there to tell, often: hard to tell where the low contact boot/binding point actually is in there, and probably often not possible to actually reach it with calipers, underneath the boot, should it be at a different depth/height than the outside, more visible and accessible part of the boot and binding. So you do the best you can: maybe different from brand or other people's measurements. (With our group of four to six, we'd usually get three or four slightly different results, which we had to learn to compare and sort out for ourselves.)
Thus the one doing the measuring can establish a consistent methodology for themselves for measuring these deltas, to at least get a set of consistent measurements to compare to actual skiing experience. That way, one can learn from experience one's preferred delta/"ramp angles" for that setup and others, by lots of experience at how the consistently measured deltas feel on snow.
(It's been my experience that I myself like different deltas for different ski/binding setups, with lots of variables involved: ski stiffness laterally and lengthwise, ski shape and construction, length, width, materials used, binding characteristics, including both delta and height, binding "give" patterns, terrain, conditions, etc. Again, lots of variables: the only way for me to sort it out is to find combinations I like, by trying them.)
) and now also am quite happy with my 175s.
