<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <body bgcolor="#FFFFFF">   Try the following for your jig... at least as I understand you..   <img SRC="cid:part1.3FD7B0CF.C816B2E8@grieg.uib.no" height=312 width=512> Also... if the length of your square is 1 meter and you place it so that it tangents the circle at its midpoint, then the end should be roughly 2.08 mm off the circle. (Assuming a 60 meter radius.) So if you have a 1 meter rib crowned to a 60 meter radius then the midpoint of the rib should be 2.08 mm higher (or lower as the case may be) then the end points.    60 - 60 Sin InvCos (1/120) = 60 - 60 Sin 89.52252964 degrees = 60 - 59.99791663 meters = 2.083369504E - 03 meters = 2.08 mm   Cheers RicB Absolute Piano wrote: <blockquote TYPE=CITE>   Given a right angle connected to the outside of an arc of a circle, how do you prove the circle is 60'? (I made a jig for crowning ribs that is adjustable and I want to calibrate it. Thanks, Jude Reveley, RPT</blockquote> -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway <A HREF="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A> <A HREF="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broadpark.no/~rbrekne/ricmain.html</A> <A HREF="http://www.hf.uib.no/grieg/personer/cv_RB.html">http://www.hf.uib.no/grieg/personer/cv_RB.html</A>   </body> </html>