Egon, There are some tricks you can do with water or other liquid, using the surface for a mirror that is essentially perfectly level in two axes. Knowing that and some trig and geometry you can sight across the surface of the liquid (using it as a mirror) and do some ratio and proportion stuff.

Celestial navigation with a sextant typically requires a clear view of the horizon at sea. On land there is no practical way to compensate for the unknown elevations of the "apparent" horizon so celestial navigators on land used to use a bowl of mercury to provide a reference to level. Its surface was flat and level and made a good reflector that would let you see the image of a navigatiional star reflected in it. As the sun is so bright, noon shots of the sun can be made with a bowl of water, provided the wind isn't too strong which makes ripples in the water.

I have done some desert navigation this way (pre GPS)

Pat [img]/forums/images/icons/smile.gif[/img]