Once the wood for the back is selected and the template used to verify that there is sufficient room for the outline, each half of the plate can be flattened. Use a jointer plane and get each half glass-plate flat. Now check to see that there is sufficient height for the arch. Measure out from the proximal border (what will become the center seam) 15mm and check the thickness of the wood at this point. Repeat on the other half. Also, check the edges to see that you have enough material for the edge thickness, taking into account that wood will be removed when the plate is flattened again after joining. Usually one half of the plate will be thicker than the other, and more often than not, rib stock can be ripped off of that half.
Set up the bandsaw with the table tilted, so that the distal edge of the plate rests on the bandsaw table. Use a block plane to clean up the distal edge so that it will ride smoothly over the table, but be careful not to reduce the width of the plate too much. The anterior aspect of the plate (the flattened side) should be resting against the bandsaw fence. Take into account the kerf thickness of the blade when plotting the cut. The rib stock, once it is ripped-off, should be between 1.9mm and 2.2mm thick at this point. (Refer to the section on ribs for a more complete description of this process.) Even if the other half of the plate doesn't have enough thickness to produce rib stock, it doesn't hurt to run it through the saw at this point. The saw is already set up anyway, and making a cut to reduce unnecessary thickness will save work later on when you begin rough arching the plate.
Click here for a video of Terry graduating a plate.