PVC Hole Scaler - The Plastic Canvas Hole/Rib Counter This is a laminated cardboard hole scaler - a plastic canvas hole/rib counter. Most measurements for plastic canvas are given in Holes or Ribs. Now you can easily count ribs or holes by counting the hash marks left to right. Each line on the hole scaler indicates a hole or rib and can be used either for 7 Mesh or 10 Mesh simply by turning the scaler to the appropriate edge. Position the Hole Scaler on the canvas so that the first hash mark (indicated by an arrow on the scaler) is centered either on the first hole or rib depending on which you want to count.