About this project
A centre finder for boards. Two pins straddle the stock, the plate self-centres between them, and the hole in the middle is exactly on centre - no arithmetic, no dividing by two, no cumulative error down a long board.
Size
Board width is the number you set; plate length follows from it plus the pins. Plate width and thickness are separate, so a wide board does not force an unwieldy plate.
Pins
Diameter and length. Length is what the pins need to hang below the plate to catch the edges of the stock, so it wants to be comfortably more than the plate thickness - the design check says so if it is not.
Pin spacing is derived, never entered. That is the whole point: the geometry guarantees the centre, and there is no second number to get wrong.
Hole
The marking hole takes a pencil or an awl, and is countersunk from the top so a pencil tip self-guides into it instead of skating.
While you dial it in
Readouts show the board width it centres, the finished plate and the pin spacing. The design check watches the sight windows, which are the first thing to disappear when the board setting is small and the pins are fat.