In the old days they drove out to the end of the runway and counted the number of runway centre(or edge)lights visible.. Knowing the spacing between them they calculated the RVR.. Nowadays itīs mostly done by a transmissiometer.. As the name suggests this is a handy little photocell operated gadget that measures a section of air to se exactly how transparent the air itself is and is then converted into a relevant RVR figure..
[ 13 December 2001: Message edited by: Brenoch ]
[ 13 December 2001: Message edited by: Brenoch ]