Marking Gauge

This tool is used to mark a line parallel to an edge. This one has a pin which scratches a mark, but they are sometimes made with a small knife blade which leaves a cleaner, sharper line. It is very useful in laying out mortises (which is what Norm was doing with it), although there are marking gauges made with two pins or knives which will mark both edges of the mortise at the same time.

The visible part of the pin here isn't the pointy part. That's below the ruled bar and obscured in the shadows.