How can you judge visibility on final using the approach lights? Is the vis good enough for Straight in? or circling approach? how to tell the difference?
Humphrey Maltman (RIP (and not due to a flying accident)) was always a big one for measuring the distance from the minima (on correct appch gradient) to the required vis and comparing this on the aerodrome plate (which is to scale) to see exactly what part of the approach lighting, number of runway lights etc. should be visible if you had the required vis.
Have heard others using rules of thumb (can see the HIALS, t'hold markings, touchdown markers).