Over the years I have noted that the altitudes given are relative to the terrain, not indicated altitude, check it out while landing, the altimeter will tell you the altitude over sea level, the "speed bar" will give you the altitude over the terrain.

That isn't true in my experience, I've crashed into the ground with a non-zero height in the speed bar many times, and quite often taken off from a height of 200 (metres I believe), in the speed bar. I don't usually use the altimeter in the cockpit for my height. The heights in the text coming "over the radio" don't match the speed bar. The speed bar, as I understand it, is the three lines of text (height, speed and heading) in the lower left of the screen.

The speedbar gives the alt from sea level, like the altimeter in the plane. When you use the view without cockpit, you have alt from the ground directly under you.
I played quite a lot offline, and it seemed to me that the indications were quite logical, but maybe it changed...

This is not what I see. I just took a Mossie over the mountains inland of Yalta, paused with maybe 100 metres clearance, certainly no more, and the speed bar height didn't change when I switched from F1 view to F2 view. If this has changed, I don't remember noticing it.

Yes, you're right but I didn't mean that, I was talking about the view with the virtual cockpit (MAJ - F1 by default, IIRC) and a sight.

I'm not sure about this virtual cockpit business. I thought F1 gave you a cockpit view? or you mean that thing with five dials and no sign of your own plane? I know <shift> (or was it <Ctrl>) <F1> centres your gunsight in planes where it isn't already centred, which the Mossie's wasn't, so I changed into that mode before doing the test.

The heights coming over the radio (maybe only for American and British missions?) are definitely weird, certainly since "1946", maybe since the "Complete Edition", could even have been as early as "Pacific Fighters" at a push. The heights don't match your height from the speedbar, which is metres for me usually, they might sort of match your height in metres converted to feet, but then the numbers in brackets seem to usually match your height in feet taken as a number and converted from metres into feet, even though it should already be feet (i.e. too high by a factor of slightly over three).

It's not a big deal for me, but when people say it isn't happening when I saw it myself, that makes it a matter for concern.

Resolved
 

I've figured it all out!

First of all, the height in the speedbar and the height in the cockpit are both "above sea level" and not particularly fine-grained, while the height in the wonderwoman/F-35 view is "above ground level" and accurate to the nearest metre.

Secondly, the height you hear over the radio isn't necessarily the height of the waypoint. They only recorded a few voice samples for height readings: 01, 05, 10, 15, 20, and so on. When the announcement comes over the radio, the game takes the waypoint height in 100s of metres, and rounds down to the nearest multiple of 5 (or to 01 if it's less than 500m). But the aircraft ignore that instruction and adjust to fly at the height of the waypoint itself.

I first noticed this when playing a Russian mission just now. There were two flights - one at 2500m and another at 3000m, and I got to hear radio traffic from both and verify their heights by flying abreast of them. It seemed like the radio was giving the right heights for once. Then I went back to the original P-51B mission, but this time I modified the waypoint heights. I've listed, in order, the waypoint height in metres, the radio announced height in metres and feet, and the height we ended up flying at:

As you can see, the height you fly at is very close (up to the accuracy of the altimeter) to the waypoint height.

A similar thing happens with the heading, but there's one of those for every 30 degrees so you're less likely to notice it. Plus, the heading only makes sense if you're starting from the actual waypoint so if you're off a little the heading will be too and it'll be your fault - not the game's. Taking the nearest reading seems like a good idea and 30 degrees seems accurate enough for our purposes.

I do wish that the game would round to the nearest sample instead of just rounding down all the time - perhaps they can remember that for the next game.

Thanks to all of you for your ideas and comments.

Check your reading skills.

As you can see from this thread, I read your post before you edited in the "wonder woman" bit. Without that hint, I took the "no cockpit" view to mean the chase (F2) view. I still read the red bit as saying something I don't see, it may be that changes in the wonder-woman view.

@ adapted.cat I like that post. That does make some sense of what I was seeing, I don't remember what it was that I saw that well but I remember it not being right, and it's interesting that 350 metres is reported on the radio as 350 feet.