If some one know
Last year, the raw marks for each paper were scored out of 60. Each paper was standardised separately then (I think) multiplied by 1.5 and added together to give an overall standardised score in the format which has been the custom over the past 10 or so years, e.g. '322.123', with 303 being the 'floor' below which you are not eligible for a place at the Southend / Westcliff schools.
If you search in the Essex section for posts by 'Aang', you will see how it is all calculated (s/he has obtained the mean scores and standard deviations for the papers from the CSSE each year for the past few years).
The maximum standardised score is usually c.420, but this is 'the score representing the highest combined raw scores', it does not necessarily mean that that child scored 60/60 in both papers and an individual standardised score cannot
be expressed as a percentage of the maximum, because it isn't.