It's hard to get pixel perfect. It's hard to see the numbers. The numbers are in the wrong spot, often in the way. I had to uninstall to look for something else. sorry.

Umm, so what is this measuring in? px? cm? Can't tell and it ain't sayin'. Replaced with Measure-it.

it doesn't work for RTL sites well.

i wish it filled the empty space with the lines and the fractions and inches so i can use it to measure multiple areas at one time. Or if i needed to make a graph.