In doing my research on proportional stringing, I realized that most of the calculators, including the one on the USRSA site, do not include the string length between the frame and the tensioning head. This will cause you to drop tension too drastically on your outter mains and all of your crosses. When you factor in the total string length and use THOSE values instead, the tension drops from the middle mains is less drastic. For example using my Volkl C10 Pro and Gamma X-6FC stringing machine: The center mains are 13.0 inches long and the outter mains are 8.9 inches long. Assuming a reference tension of 60, most calculators will tell me to pull the centers at 60 and the outters at 41 [60*8.9/13.0] the other mains at descending tensions in between. This gets even worse when you calculate the crosses. The center crosses are 9.5 inches long and the shortest cross is 6.5 inches long. Running the same math, the cross tension starts at 30, increases to 44 at the center and drops back down to 30 at the throat. Now, if you factor in the string between the frame and the tensioning head (on my X-6FC anyway) the center main string length is 20.1 inches long and the outter main is 16.5 inches long. Using the total string lengths, the calculator tells me to pull the center mains at 60 and the outter mains at ~50 [60*16.5/20.1]. That's a 9 pound delta over the example above! Doing the same thing on the crosses yields a range from 42 to 54. That's a 12 pound delta at the edges and a 10 pound delta at the center! Be careful using the calculators when doing a proportional string job and use the TOTAL string length for the string being tensioned, not just the string length inside the head. As the frame rotates around the table, the length of the string inside the frame AND the string from the frame to the head changes affecting the tension. The range of length change from the tensioning head to the frame can vary by more than inch. If racquets were perfectly round, this would not be an issue, but they are oval and the distance to the head varies significantly.