Well, I used the trusty old whizz wheel to plan my flight to Old Warden on Sunday. My landing slot was 1120Z, so I knew that to make the overhead at 1115 I was going to have to leave my timing point (WCO) at 1059. Did this, overhead on time, landing would have been spot on - BUT for some ignorant turkey who blundered in without checking, joined downwind ahead of me having clearly not bothered to read the arrival instructions (Overhead join
mandatory) and then flew a typical excessively long final!
The GPS agreed with the whizz-wheel, but it's important to be able to fly the plan even if the GPS dumps. My forecast wind estimate of 230/15 was pretty close - so I stand by accurate pre-flight planning using the most accurate information available being the best way.