Actually, the calculation of the FSIQ from the Sum of Scaled Scores isn't magical (nor proprietary). No table is required as there is a simple one-to-one correspondence between the Sum of Scaled Scores and the FSIQ. It would be the same as someone calculating the Percentile Rank from a Composite Score. It is just basic statistics.
FSIQ = 25 + 0.75*S where S is the Sum of Scaled Scores.
Here's the statistical reasoning for anyone interested...
The Sum of Scaled Scores is the sum of the 10 Subtest Scaled Scores. Each Subtest Scaled Score ranges from 1-19 with a mean of 10 and a standard deviation of 3. Each is assumed to be normally distributed. The Sum of Scaled Scores follows a normal distribution with a mean of 100 and a standard deviation of 20. The only difference between the Sum of Scaled Scores and the FSIQ is that the FSIQ has a standard deviation of 15 (not 20). You can easily convert from one normal distribution to another, so if you know the Sum of Scaled Scores, you know the Fulll Scale Composite Score (FSIQ):
FSIQ = 100 + ((15/20)*(S-100)) <- same as above, before simplication
The 100's are the means of the two distributions and the 15 and 20 are their standard deviations. All of this can be obtained by publically released information.
