You're correct, there is no '3D ruler' but instead we enable you to break it down so that you can build a mock up of the build onto the plate as shown in e1 on the pictures.
To expand on this a little, with the example with the CPU block and the fitting on the side, you would simply measure the vertical height but using 2 rulers (by the looks of that example it would be the shorter one plus a longer one) to get the hight of the fitting. This would be your first 90 degree bend that goes in parallel. You can actuaally add this to your mounting plate included in the Eiskoffer if you like. Next just flip the ruler 90 degrees and measure from the fitting to center of the other fitting.
It does seem a lot more complicated, but once you get the hang of it it is just as easy. Quite often with '3d rulers' there are other components in the way, or you can't quite hold everything hence the lack of a 90 degree bracket.
Having said that, this is the first time this has been mentioned to us from a customer so I will pass it on. If one customer thinks it, usually many others do and we always try and make our customers happy