Hmm, I thought whatever the cephalometric landmark, horizontal + means forward and - means back. Vertical + means down, - means up. It sort of makes sense + for downgrafting, advancement, - for impaction, setback.
The A-P for BOTH maxilla and mandible is more straight forward/consistent where a + is horizontally forward in both and a - is horizontally backward in both maxilla and mandible.
Now vertical directions (+ or -) for the MAXILLA are more straight forward too because when we see a + sign for the PNS (as in posterior downgraft), we know the + sign refers to that area (and all other areas to the maxilla with a + sign) being moved
down. Hence a - sign for the maxilla refers to that area being moved up. But that's just for the maxilla.
Now for the mandible it's reversed. A + sign refers to an area moving vertically up and a minus sign refers to an area moving vertically down. Well, at least that has been the case of other cephs displacement diagrams I've looked at where the read outs give a + or -.
So, other people's ceph displacement diagrams where you can look at both the + and - directions for the mandible show that a - sign means downward vertical and + means upward vertical.
If you look at other people's ceph displacement diagrams for the MANDIBLE where they also give the read outs, you will see that something going vertically DOWN is marked with a - sign and something going vertically UP is marked with a + sign.
So, NO IDEA why the OP's vertical readout for the mandibular displacement were all - (negative signs) when that usually means vertically DOWN because the ceph displacement diagram shows all the parts moving up. Maybe they reverse the signs for anterior impaction but IDK.
Oh well, NEXT TIME, I shall request people put up the WHOLE document where both the displacement diagram and the read outs can be seen together.