The crack gauge helps determine the width of a crack by comparing it to the printed lines on the card.

Left Side: 2cm Scale
Right Side:1in Scale
Top: 3/8", 1/4", 1/8". 1/16", 1/32", 1/64", 1/100", 1/200"
Bottom: 1.5mm, 1.25mm, 1mm, .80mm, .60mm, .50mm, .40mm, .30mm, .20mm, .10mm