Just to expand on that, usually the etched scale pitch is 20 microns, but digital quadrature detection gives you 4x the resolution of the scale pitch, resulting

Just to expand on that, usually the etched scale pitch is 20 microns, but digital quadrature detection gives you 4x the resolution of the scale pitch, resulting in a 5 um distance between successive rising / falling edges of the quadrature signal. Analog measurement can be used to interpolate to much finer resolution, even 1 nm for good quality optical scales with good electronics.