NavList:

I have some issues with these floating mirror artificial horizons. First, normal mirrors are made flatness tolerances unknown to us, me at least. However, they are the best we have without going to optical quality first surface mirrors, after all it's only for practice anyhow. Secondly, gluing mirrors to some flotation device cannot be done uniformly, varying thickness of glue, varying pressures during gluing etc. Thirdly, varying flatness of the surface of the flotation devices. Fourth, variations in the density of the flotation devices, be it foam, wood or whatever, will affect the height it will float in the liquid affecting the levelness of the top surface and mirror. I think any measurements taken with floating mirrors should be done twice in opposite orientations as Greg suggested. I think floating mirror systems are really introducing more errors. Just my thoughts as an engineer and amateur navigator.