"John Gaquin" wrote in message
...

When I learned to fly in the Denver area, I got accustomed to wx reports
that included "clear and 70". The guys in the tower at Stapleton would
just look south. If they could see Pike's Peak, the vis was 70. Easy.
Infallible. No gizmo to break.


Being able to see an object 70 miles away does not mean the visibility is 70
miles. Prevailing visibility is what is reported, that's the greatest
distance that can be seen throughout at least half the horizon circle, not
necessarily continuous. If Pike's Peak could be seen but the furthest
object to the north west or east that could be seen is five miles away then
prevailing visibility is five miles, not 70.