Check the sharpening
The blade edge checker, GBC, is a tool for checking the sharpening on blades that are side-honed. It is a fast system for seeing whether the grinding goes straight or diagonally across the skate blade.
Place one of the grey parts at the front of the skate blade and the other one in the back. Use a finger to flip them slightly so that they come into oscillation. Read the result when the oscillation has stopped. If the angles of the parts are different, the grinding is diagonal.
Important! Use a whetstone on the skate blade before you use the GBC. Otherwise the measurement can be skewed.