ASME B89.1.2M pdf download Calibration of Gage Blocks by Contact Comparison Methods (Through 20 in. and 500 mm) 3.4 Micrometer Unit The metric unit representing one millionth (1/1.000.000) of a meter was formerly expressed as onemicron,*and identified symbolically by the Greek let-ter u (mu). It has been replaced by the name “microm-eter’and identified by the symbol um, For reasons ofclarity...