Relates to engineer's comparators having magnification factors from 250 to 10000 and over. The type fo comparator to which This Standard is primarily intended to apply is an instrument which comprises a rigid stand supporting a measuring head over a work-table. The measuring head is provided with a measuring contact whose movements are amplified and indicated on a scale. The means of amplification may be mechanical, electrical, optical, fluid or pneumatic. The values of the divisions and the range of the scale are determined by the sensitivity and range of the measuring head. The distance between the measuring head and the work-table is adjustable to suit workpieces of different sizes up to the recognized capacity of the instrument. The scale may be graduated in inch or metric units or in both inch and metric units.