On Wed, 10 Nov 2004 14:47:56 GMT, "William W. Plummer"
wrote:

Just how does modern surveying equipment work? One guy holds one of
those mirrors (actually a prism) that reflects light back to the source,
independent of the angle of the mirror. The instrument head contains a
laser. Distances must be measured by angles, but how?

Speed of light?

all the best -- Dan Ford
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