It has been worked out by this formula:
Quarterbacks average over the THA, SAC, MAC, DAC and Throw on Run attributes. Tom Brady's is 86.6 which we round to 87. 87 is what you set the CPUs accuracy if they are controlling Brady. The HUM accuracy is the difference between the CPUs accuracy and 100. So 100-87 = 13 which is what you set the HUM accuracy too when you are controlling Brady.
You don't need to worry about this though, use the Chart. I have done all of the sums for you
