I start by fitting a piece of the milled rail stock to the edge of the panel and useing a fine point drafting pencil to mark the panel to indicare the amount of wood to be removed. Then I use a depth gauge to measure this dimension and use the depth gauge to set up the blade on my table saw.
I make one test cut. The final cut will be done in two passes, here I make just the first cut, and only part way along the panel edge. Just enough to do a test fit. Perfect!
This will work great for Jeffreys tables, but Shelly's are considerably larger, so my standard measurement go out the window and I break out the calculator to use relational fractions to determine what the proper lengths should be for those. Then I'll cut another backer board and mark those dimensions on it.
I'll cut a test set, fit them to the panel and see how they fit. If adjustments are needed, make them. When the fit is right, cut all the rest to the same dimensions.
Thanks for reading!