In days of yore, (groan) the braking action at a lot of airfields was assessed by driving a Land Rover onto the runway, and standing on the brakes with a mu meter?..or whatever. One thing is for sure, I would prefer to see for myself what conditions were like on the runway in some remote airfields.
Where the tires actually tracked was important to me, if I was to get a meaningful reading.
I recall being at ( a lonely regional) with a load of pax that had nowhere to go in thick snow. Breaking action did not respond to the urea treatment, until the last bag! We just got the reading we wanted to be legal. Nice as the folk were, I was glad that it was I, that actually took the reading. And no, I didn't cheat.
(The only really hairy thing that night was the F/Officer walking along the top of the wing with a broom. An heroic effort, but one that I would not have let him do had I known.)
Things have changed hugely now, and most of you will cry ‘thank heavens', but as implied earlier, in the early days, there was probably more learned ‘in the field' than would be allowed now. And hey, a lot of what you are taught as theory now, was learned the hard way by the post war bunch.