Easily mark your filament and then confirm with this tool. keep sharpie ink or paint pen off your calipers or ruler. Using 6" calipers to measure filament to mark it can be awkward or clumsy for me. The notch in the tool also keeps your filament straight for higher accuracy. print tool on it's end with the 20mm bar downward on build plate, use tree supports and brim. You will have a good experience!