Capatch is a one-time-use tool that works by contact with the roll as a kind of sticker. A calibrated amount of indicator fluid contained within a capsule on the sticker is forced across the roll under the Capatch sticker when the user runs across the surface with a blade, known as the doctor blade. The blob of indicator fluid breaks through the front of the capsule and is pushed into the open cells of the roll by the doctor’s blade. The liquid blob first fills the cells nearest the capsule, decreasing in volume as it is pushed forward until the entire volume of the blob has vanished into the roll cells. The length of the liquid track determines the current volume of the open cells of the roll. Since the volume of the indicator fluid is constant in all Capatch strips, the length of the track is inversely proportional to the ink, adhesive, or coating volume of the roll cells.