Ah, thanks for the correction on "conning tower" rocket.
![Smiley :)](https://models.rokket.biz/Smileys/default/smiley.gif)
This forum is great for learning something new almost every time I log in.
Yeah, navigating across the water is a lot more complicated than on land. True vs magnetic north, variation and deviation are just the beginning of the navigation courses I took and actually some of the easiest parts of it. I still have 2 years to go to get the celestial nav part down, but since I've only sailed on the ocean within about 50 miles of the continent, I don't think I need those. After all, even if I got lost, just head west and I'm bound to find N. America eventually, right?
BTW, the two balls in your pic are called "Flinder's balls" after Cap't Matthew Flinder, who was the one who invented the idea. They're made of soft ferro-magnetic iron, and they're mounted on little slots in the arms ao they can be slid in and out. You'll only find them on the binnacles of steel hilled ships, even in WWI torpedo destroyers, dreadnaughts, monitors, etc. (all these interesting types that we no longer have) so if you ever do a model of a tall ship, make sure you know what the hull was made of (or in the case of a ship like say, Cutty Sark, where the hull was wood but the frame was steel, so it would have had Flinder's balls).
Anyway, how they work is that as I'd mentioned before, in a steel hulled ship, there's more mass of metal lengthwise along the direction of the keep than there is athwartships, and that means the compass deviation is greater when the keel is lined up with magnetic north than when it's pointing east or west. The Flinder's balls compensate for this by adding to the metal abeam of the compass, but they're placed much closer to the compass so even though small, their affect is greater.
Note also that the post in your binnacle picture is wood. You don't get metal binnacles until more modern times when aluminum became sheap enough to make binnacles out of that. I think some old ships might have had brass binnacles, but that would be a rarity.
My own boat haas an aluminum one but I made a teak covering for it to make it look reminiscent of the old style in your picture (only a LOT smaller!)
Oh yeah, the reading being backward in the binnacle you see would be specific to the design of that particular ship because of where the helmsman was expected to stand for whatever reason. Some are backwards, most are regular. Most mag compasses have different posts and markings on them to help read the direction from different positions around the compass, depending on where the helmsman is standing at the time. On my own boat, the entire top is clear, like a snow globe, so I can read it from 360 degrees around. About half the time, I wouldn't be standing directly behind because if the boat is heeling, it's just too uncomfortable so the helmsman might sit off in the corner to one side or the other where he has a backrest and cushions and better visibility forward around the mast.