Colen Clenton recalibratable squares and markers are very unique because if they are knocked out of square they can be recalibrated back to square. The adjacent photo shows the quality of workmanship and engineering involved with making these squares recalibratable which ensures you have a lifetime tool. Readjustment is easy and instructions come with the tool showing how it is done.
The blade is in the middle of the handle to provide bearing when marking out on either edge of the board. Square on the bottom of the blade for marking out the dovetail on the end of the board and checking inside the dove for accuracy.