GLASS INSPECTION/CALIBRATION PLATE IN LIKE NEW CONDITION! 
15/16" THICK,  18" x 18"
CAME FROM CORNERSTONE METROLOGY SERVICE IN VAN NUYS, CA 
PURCHASE DATE IS 4/10/2001
DON'T KNOW HOW MUCH OLDER THAN THAT, THAT IT IS BUT THE PLATE ITSELF AND THE BOX IT IS STORED IN IS IN BEAUTIFUL CONDITION
NO RETURNS PLEASE