25×,40×and 100×measuring microscope are kinds of precision optic measuring instruments,They have medium magnification that are between normal magnifiers and tabel microscope.Their portability is much betterand easy to use with high precision reading.Mainly used in diameter or length measuring of miniobject(less than 7mm).With the external illumination attachments,their using is not limited by enviroment brightness.The most characteristic of these instruments is that length or size of the observed object can be read out directly in metric(mm)of imperial(inch).