With the purfling in, I now start on getting the arching to its final, or at least nearly final, state. I use templates, based on the original instrument, in this case the Stradivari 1715 "Titian", but cleaned up with curtate cycloids. Curtate cycloids are similar to what people of my age might remember as a spirograph, and are an old mathematical form, certainly known in the time of Stradivari and Amati. To draw a curtate cycloid, you can take a button. Put a pencil through one of the thread holes, run the button rim along a ruler, and trace out the pattern on paper.
While planing down to the final arching, it is satisfying to pull up a fine strip of the purfling as you go.