In all truthfulness, when measurements are taken and the rides are different from the advertised numbers, it isn't because the advertised numbers are necessarily wrong. The Big One, for instance, was advertised in terms of its height from 'ordinance datum' which is the standard 'zero point' for any construction in England. So it is a perfectly fair comparison and a perfectly accurate comparison with any structure constructed in the UK because it defines the ride's height relative to an absolute measurement point. Different agencies use different measurements. For instance, I believe Guiness measures from the height of the track in the station to the height of the track at the top of the lift. This would put at a disadvantage a coaster such as Steel Phantom, which has the station in the middle of its vertical spread. Other agencies may measure from the top of the lift to the lowest point on the track. These kinds of discrepancies can possibly account for, for instance, Millennium Force growing by 11".
--Dave Althoff, Jr.
