a unit of length equal to one millionth of a metre, used in many technological and scientific fields.
a gauge that measures small distances or thicknesses between its two faces, one of which can be moved away from or towards the other by turning a screw with a fine thread.
A measure of length; the thousandth part of one millimeter; the millionth part of a meter.
An instrument, used with a telescope or microscope, for measuring minute distances, or the apparent diameters of objects which subtend minute angles. The measurement given directly is that of the image of the object formed at the focus of the object glass.