This very good question just recently came in, from a music educator:
I am seeking any resources on French horn tuning, including diagrams with slides labeled and suggested amounts to pull each slide and the process of tuning to give to my students. I know different brands also have different slide locations, so if there is access to that information in other brands (Holton, Hoyer, Yamaha, etc.) that would be great.
The answer is a little complicated. It would be great to have such a resource with details on a wide variety of popular model horns, but unfortunately it would be almost impossible to do in a way that got down to very exact measurements.
Slide positions will vary due to variations of instruments and variations of mouthpieces and players. How you place pitches on an instrument will influence where the high range lays relative to the low range, for example, not to mention hand position variables as well. Then let us say you have a 1955 Conn 8D and compare it to one from 1985 and one made last week. The exact slide positions will certainly not be the same, and some might not be at all the same, as the old Conn’s had a longer main slide (which I wish the current ones had).
Fortunately, an experienced horn teacher will have a good idea of a typical setup for popular model horns. But for music educators or horn students not certain how to tune your horn, there are a few Horn Matters articles related to specifics on tuning, in particular,
The second article above mentions that I used to have a lengthy article online on this topic; that text, as of 2018, is incorporated into my high horn book, as sharpness in the high range is a frequent high range complaint.
For a similar article on tuning double horns in general, the classic article by Philip Farkas on this topic in The Art of French Horn Playing is hard to beat.
However, as already noted, keep in mind that every horn will vary a bit. Perhaps some Doctoral student might try to address this in a project, it would be a helpful one to the horn community.