Standardisation is complex formula to compare and rank test takers. In really simple terms, it uses the average (%) score of a group and then plots the standardised score against that average. Usually the average standardised score is set at 100 as below but if you are in Bucks it is set higher (from memory I think it's 111)..
Fuller explanations can be found herehttp://www.elevenplusexams.co.uk/standa ... scores.phphttp://www.nfer.ac.uk/nfer/research/ass ... sation.cfm
Edited to add. In Essex they standardised the scores without any adjustment for age. So lots of regional variation on how standardisation is performed.