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The AS number stands for American Standard, and is “AS” (or “American Standard”) followed by a number indicating the position in which the glass may be used, based on its optical quality. AS1 is the clearest glass (at least 70% light transmission), is laminated, and can be used anywhere in a motor vehicle (typically just the windshield), AS2 is tempered with at least 70% light transmissions, and can be used anywhere except the windshield, and AS3 can be used in certain locations in certain vehicles (and can be laminated or tempered, and has less than 70% light transmission). There are higher numbers used for other purposes, but are not normally encountered in cars. This number must be near the manufacturer’s name/logo, preferably below it (per Z26.1996 - See more at: http://www.carwindshields.info/windshieldmarkings#.dpuf