Search Ebay for "machinist's straight edge". The prices are ranging from less than $20.00 to over a thousand, depending on how precise you want to be. It looks like some in the $40.00 range might be something I'd be interested in having, particularly the 3-sided one from Belarus.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!