OK that's awesome, I'm totally happy for people to be able to make their way around without the clues! There'll be some locations where it'll be quite difficult to find without the mapping, but in that case they're kind of bonuses either way!
I'm also thinking some environmental clues might be nice for hinting at wind. I'll definitely have to have clouds in some form so that'll help there too.
Calipers definitely look similar but they're for measuring width/length. I did research into cartographic instruments and I think the closest thing is maybe an octant or sextant, but honestly I think my instrument is unique mostly because it wouldn't actually be very useful in real life :p