They take your scores on each section of the test, combine them in different ways to get each rating, and rank you on a bell curve compared to everyone else that takes it. Your score in each section is determined by regions of your percentile on the bell curve.
Each one is supposed to be a predictive indicator of your performance in different jobs I guess, out of a possible 9/9/9/80:
1. Academic Qualifications Rating (AQR) : This score is affected by performance on all sub tests, but the strongest influence is made by the Math Skills Test.
2. Pilot Flight Aptitude Rating (PFAR): This score is affected by performance on all sub tests, but the greatest contribution is made by the Aviation & Nautical Information and Spatial Apperception Tests.
3. Flight Officer Flight Aptitude Rating (FOFAR): This score is affected by performance on all sub tests, but the strongest influence is made by the Math Skills Test.
4. Officer Aptitude Rating (OAR): This score is affected by performance on the first three sub tests, Math Skills, Reading Comprehension, and Mechanical Comprehension.