The preferred location to measure warp (bow, crook, and twist) is on the planer outfeed belt, after the GradeScan scanner. The mechanical impact to the mill is very limited, and the results are excellent since boards are relaxed and not constrained by rolls.
Lucidyne’s Warp Tunnel requires minor changes to the outfeed belt itself, typically just cutting some slots in the conveyor sides. It is far more accurate than attempting to measure warp while boards are being transported through rolls in the scanner itself since the boards are relaxed and lying on the flat belt. The Warp Tunnel scanning equipment takes up six feet along one side of the belt and is located in the middle of the conveyor to be away from the ends of the belt.
The picture below shows a Warp Tunnel mounted on an outfeed belt in a southern mill.
Here is another example of Idaho Forest Group's Warp Tunnel in application.