Well that’s not entirely true, of course. I do use them when I need to make up a cut list from a full-scale drawing or story stick to tell a machine in numerical code (be it metric, Imperial or shaku) where to make the cuts. The cut list is, however, rarely necessary in the hand-tool approach to construction. So in typical layout work, I go with pin-point perfect real placements of cut or location lines.
For example, if I need to lay out the location of slats in a bed’s headboard, I simply stack the slats together against the post (or its location on a story stick) and find the intervening gaps by stepping out the number of gaps needed between the slats (number of slats + one). Layout follows as shown in the next drawing. The accuracy of the layout will be a function of however sharp I make the points of my dividers.
Of course, you can use algebra to generate dimensions with numbers:
As for me, I don’t want to spend the time doing it and then having to deal with reading tiny numbers on some ruler and coping with rounding errors!
As another example of rulers not always ruling: Say you want to locate placement buttons (the ebony plugs in the set shown here) on a pair of winding sticks so you can quickly locate the sticks on the edge of a board. In this case, the location is not a number at all (at least not until after the fact). You could, of course, measure the length of the sticks and divide by two to get a numerical center point. Or, to avoid rounding error, you could step off an even number of intervals to locate the middle division line and then enjoy the accuracy of a pin prick. But both would miss the point so to speak. What we are really looking for here is not the center of the stick, but its center of gravity. How do we find that? We just balance the stick on a sharp knife blade!