These UPC symbols offer various grades of void defects for use in testing bar code verifiers. Each symbol is individually calibrated to ANSI X3.182/ISO 15416 standards using a custom built microdensitometer. These cards are supplied calibrated for use with a 6 mil scan aperture and 660 nm wavelength. .(calibration with other aperture sizes or wavelengths is available) Each card is laminated to an opaque backing, to prevent reflectance changes from placement on various surfaces. Cards are available in a range from Grade A to Grade F (Iso Grade 4.0 to 0.0). The images are precisely created in photo-emulsion. To achieve a void defect , one bar has been altered to include a precisely thin white line in the center of the bar (the whole symbol height, from top to bottom). % The precision of this line causes the defect grade to be the same no matter which scan path is used to scan the symbol. Each card is individually serialized, major values are marked on the card, and all values are included in a written report.