I’m informed that the MacBook Air’s solid-state drive option fits the SAUK model precisely, with no rounding: 110% of (117.5% of (US$3098 in UKP ~= £1569)) = £2028. And Apple doesn’t always round upwards, it seems: the US$99 external SuperDrive comes out at £65.33 before adjustment, and is apparently being sold at £65 rather than £69. What charity.

Reaching back to my mostly forgotten maths classes, you can simplify the calculation to a standard Apple British Coefficient of 1.2925, for those who don’t get to buy ex-VAT (or, more likely these days, on a weekend in NYC).