The raw scores go through a statistical process called standardisation which starts by looking at the average of the raw scores for this exact test. Okanagan posted a nice explanation in the Warwickshire forum here. viewtopic.php?f=37&p=329502#p329502
The standardisation is done by age, so older children compared against older children, younger against younger to make it fairer.
At the end of the day, all the raw scores will be translated into standardisation scores, one for verbal, one for non-verbal and one for maths. These three scores are then combined by "weighting" so that verbal will contribute to 50% of the final standardised score, non-verbal 20% and maths 30% giving an overall final STTS (standardised transfer test score). This is the key number.
This year the STTS scores for Bucks will be more spread out than in previous years, they will range from 40 to 180+, and in theory the average is 100 (though it's not always been in Bucks and figures like 110 have been mentioned). An overall combined STTS score of 121 or more will mean the child does qualify for Grammar schools. It doesn't matter if it's 121 or 180 both qualify equally.
This year hopefully the spreading out of scores will work so we should expect less people to achieve 120 and 119 etc making it easier for selection reviews and appeals to differentiate between the near misses.