ASTM B487-85 pdf free.Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section.
Any error in calibra-tion of the stage micrometer will be reflected in the measure-ment of the specimen. Errors of several percent are notunrealistic unless the scale has been calibrated or has beencertified by a responsible supplier. The distance between twolines of a stage micrometer used for the calibration shall beknown to within 0.2 um or 0.1 %, whichever is the greater. Ifa stage micrometer is not certified for accuracy, it should becalibrated. A generally satisfactory means of calibration is toassume that the stated length of the full scale is correct，tomeasure each subdivision with a filar micrometer，and tocalculate the length of each subdivision by simple proportion.5.10 Calibration of Micrometer Eyepiece:
A filar micrometer eyepiece generally provides themost satisfactory means of making the measurement of thespecimen.The measurement will be no more accurate than thecalibration of the eyepiece. As calibration is operator depen-dent, the eyepiece shall be calibrated by the person making themeasurement.
Repeated calibrations of the micrometer eyepiececan be reasonably expected to have a spread of less than 1 %.5.10.3 Some image-splitting micrometer eyepieces have anonlinearity that introduces an error of up to 1 %for shortmeasurement distances.
Errors can be introduced by backlash inthe movement of the micrometer eyepiece.If the final motionduring alignment of the hairline is always made in the samedirection, this error will be eliminated.Because the magnification may not be uniform over the entire field, errors can occurif both the calibration and the measurement are not made overthe same portion of the field with the measured boundariescentered about the optical axis.Lack of sharpness of the image contrib-utes to the uncertainty of the measurement. Poor quality lensescould preclude accurate measurements. Sometimes imagesharpness can be improved by using monochromatic light.5.14 Orientation of Eyepiece -The movement of the hairline of the eyepiece for alignment has to be perpendicular to theboundaries of the coating cross section. For example,10°misalignment will contribute a 1.5 % error.ASTM B487 pdf download.