Sometime ago we were fortunate to have a beautiful Guarneri Del Gesu violin in the shop. We photographed and took measurements of it to keep on file. As I make instruments in the workshop I often refer to photographs and other information for inspiration or to copy. I also keep records of my own violins as I make them. It’s an important part of most modern violin maker workshops. For the Guarneri we also measured the thickness of the back and front of the violin.
To measure the thickness we used a hacklinger gauge (shown below) at numerous points, spaced 1cm apart over the entire surface of the back and front of the violin.
To be precise about the location of each measured point, we laid paper over the back of the violin, printed with a grid pattern. (available online from incompetech.com) I used the hacklinger gauge to measure each point printed on the paper, while my assistant wrote down each measurement. We factored in the thickness of the paper (.1mm) that we had laid over the violin. Once we were finished we had a page of measurements (in mm) like this:
While this might be interesting information, it’s difficult to make sense of all those numbers. I like to have a feel of the overall concept of a great old violin, not just the thickness of a particular point on the back or front.
To help visualize the thicknesses, a colleague Hans Pluhar wrote software (available at violingraduation) that allows these measurements to be turned into “Colour Graduation Maps”.
Yellow being under 2.5mm and purple over 4.5mm. 
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Using the software I’ve made thickness or graduation maps for the workshop. Below is a part sample of one:
Now the thick area in the centre of the back is clearly visible (in dark blue and purple). The thinner green areas are also clearly defined. How I interpret and use this information while making a violin is another subject. But having this information, from great sounding instruments of the past, has been helpful in deciding what concept of thickness I might use in my own instruments.
