This way of clamping with string and a dowel is very simple, it applies plenty of clamping pressure to the glue joint and it is light weight.
I was introduced to this way of clamping ribs to the blocks by Joe Grubaugh at Oberlin this year. I was amazed. The way I was taught to clamp ribs at violin making school was with metal clamps and cork lined counter parts. I was taught to build my rib structures on a flat piece of glass as well. This way is very precise, and not the way the Italian masters built their ribs.
In the Museo Stradivariano in Cremona, Italy there are several surviving forms from the Stradivari workshop, as well as wooden dowels and counterparts. We can assume that this is how Stradivari, and most likely the other makers in Cremona, clamped his ribs.
When making a violin in a particular makers style it is extremely important to try and understand how that maker worked. I am a firm believer that the stylistic development of any maker is founded on their tools and how they worked with them. In as much as I can, I try to return to those methods in an attempt to get similar results.
Here is a video of the knot I use to tie the ribs to the form.