RzB wrote:
Many thanks to all for the responses.

One other point - The Distance:Spot ratio. Do I take it that's
the size of the area being measured vs. distance from surface?
So if it's 8:1 then if you are 8 metres away from the surface
it's measuring a 1 metre diameter area.

Many thanks,
Roy

No, it's in mm, you can be 800mm away and get a 100mm feild in which
readings can be taken, sort of like a torch beam.

It won't pick up anything from 8 metres away because it's over 26 feet.