"Will Janoschka" <email@example.com> wrote in message news:DmJ5SKFdRQph-pn2-QUggUOhLbgsZ@209-142-179-188.dyn.centurytel.net... > On Tue, 2 Apr 2013 14:27:30, "Tom Potter" <firstname.lastname@example.org> wrote: > >> >> "Will Janoschka" <email@example.com> wrote in message >> news:DmJ5SKFdRQph-pn2-FrKUY0f5BCdS@209-142-179-211.dyn.centurytel.net... >> > On Tue, 2 Apr 2013 09:07:58, "Tom Potter" <firstname.lastname@example.org> wrote: >> > >> >> How would one measure a right angle >> >> without using geometry, >> >> or the 3-4-5 relationship, >> >> >> >> and how precisely can a right angle be measured? >> >> >> > Optically to about an eighth wavelength, for all >> > three right angles of a corner cube. >> > Is that close enough for government work? >> >> What are the optics based on? >> A measurement, a theory or on geometry? > > A measurement. A corner cube, 3 orttogonal > right angle reflectors, reflects light to its orign over > wide angles and reverses parity, Optically, any > deviation off any angle results in multiple images. > The onesleft on our moon were good to 1/4th > wave visable They have distorted some over time.
How do they measure the right angle, what do they use as the right angle reference, and what units are the deviations from a right angle in?