1. Place the measuring tool at the base of the knob, where it meets the surface it is attached to.
2. Extend the measuring tool to the furthest point of the knob, perpendicular to the surface.
3. The measurement you obtain is the projection of the knob.
Here are some additional tips for measuring the projection of knobs:
* Make sure that the measuring tool is straight and parallel to the surface of the knob.
* If the knob has an irregular shape, you may need to take several measurements and calculate the average.
* If you are measuring multiple knobs, make sure to use the same measuring tool and method for consistency.
By following these steps, you can accurately measure the projection of a knob for installation or replacement purposes.