What is a microinch?
A microinch (µin) is the inch with the SI prefix micro, meaning one millionth, so 1,000,000µin make one inch.
The microinch is mostly seen in surface finish. US drawings give a part's roughness (Ra) in microinches, and a typical machined finish is 63µin, or 1.6µm.
A microinch is a millionth of an inch, which is exactly 0.0254 micrometers or 25.4 nanometers. Outside the US surface finish is given in micrometers instead.
What is a meter?
The meter is the SI base unit of length and is equal to 100 centimeters or 1,000 millimeters. It was originally defined as one ten-millionth of the distance from the North Pole to the equator along the meridian through Paris. Since 1983 it has been the distance light travels in a vacuum in 1/299,792,458 of a second.