Spiling sticks, joggle sticks and a “digital” rule

[Philip Davies]

I could not see the point in using such a spiling stick in your example. Why not just use a pencil to draw around the object's profile?
I assumed it could be used on larger (longer) items, i.e. boat building, where tracing a profile to a "template" is beneficial. This prompted me to look on Wikipedia spiling stick which shows the intended use, though with a different "stick".
I further assumed that the notches are more for creating a line or mark at specific distances from the edge being profiled. Hence the taper of the stick.
So, instead of using the point as an indicator of sorts, the "back" (unnotched) edge is moved across the board being profiled and the pencil or other marker placed in a suitable notch, is moved along/across the template. This generates an appropriate "cut" line for the template or the new board that fits against the previously "profiled" board. Obviously in boat building this is a useful tool, for smaller items, perhaps not so useful.
Best wishes...

Yes, I take your point, Peter, ha ha. I could not think of anything else to use as an example. It was merely to show the technique. The last time I did this was to fit an oak window board into an irregular masonry opening.

Were you to fit a board to fit the bottom of this ( slightly tapering) chest I made, you might find the method helpful. While I might scribe using compasses, it’s never occurred to me before to move the spiling stick and pencil simultaneously