Hi lensman57,
You'd better ask hareng about the "radar outdoors" as they are apparently the only ones that you can trust.
He claims that turning on a light will make all others read 18 - 24 fps fast but doesn't say whether that is irrespective of calibre, pellet weight, design or muzzle velocity!
Even if that were true, it should only mean that you would turn down your muzzle velocity by a few percent, thereby increasing your margin of safety from prosecution!
He may also inform you that the police do not test rifles using Skan units but send them to the lab for a fee of £500.00.
It's good to see tax payers money being used so freely when they could buy their own Skan for £200.00! ;-)
I too have a Combro and now an R2A. They have so far read consistently within 4 fps
of each other on my 0.22" at around 600 fps.
That is within 1% which is good enough for me.