Nice bit of kit. Note the bit about testing to 80 mph. I had looked at their 2006 user manual earlier today, and it said the same thing. CAP 683 doesn't actually give a specific speed for runway friction testing, but perhaps I can help. 40 mph is for roundabouts and shopping centre carparks. 40, 60 and 80 mph are for airports. If the runways are grooved, then the 40 and 60 mph speeds can be used to infer high speed wet friction. If they are not, then I rather think the 80 mph speed test is needed.