"Although it was not a mechanistic process, a judge should approach the sentencing of a young offender in the following way: first, it was essential to work out what sentence would actually have been imposed on an adult. That meant identifying the appropriate starting point, then determining whether that notional sentence went up or down according to the aggravating and mitigating factors and then reducing the sentence for a guilty plea. Only after that should the youth discount be imposed. That had the advantage of keeping firmly in mind what the actual sentence of an adult would have been before discounting for an offender's age ensuring that the objectives of the guidelines were achieved."