That's ridiculous, it's just to give them more leeway, the queue boards at Thorpe are always woefully unreliable and I find are more often than not completely inaccurate. I really think at all the Merlin parks, but more Thorpe, the system or a similar system to the one at Disney needs to be used. Every so often a member of staff at the entrance to the ride will hand a card to someone entering the queue, just before they ride they hand this to a member of staff in the station, they then scan it in and that figure is then advertised , maybe with 5/10 mins added to allow for delays etc.It works excellently and you can always trust that the queue is near enough to what is shown.Also I agree with Themeparkmad, 0-30 is not quiet. 30-60 is not average and 60+ should be extremely busy.