Duffy scale is when you measure the height of a wave that is how high the wave is.
If a wave is 3 feet high from the bottom of the wave to the top of the wave it is determined to be “3 feet”.
The wave face is where this measurement is taken because that is the part you surf on.
If you are 6 feet tall and you stand straight up while at the bottom and the wave is determined to be head high then it is a 6 foot wave.
I know this is complicated and, for some, counterintuitive to use an objective measurement system to determine wave height. I understand that it’s more core to take the actual wave height and call it half as high as it actually is.
This type of measuring is also how we end up with "100" foot waves at that mushburger show off picture spot in Portugal. Where a "100" foot wave realistically has 150 feet of face, because the wave is slanted and you're taking measurements from the front as if it were one dimensional, but only has 20 feet of rideable wave, because the rest is nearly flat water.
I think of this because of one day when a person i was talking to claimed that the waves were over ten feet, and they had proof, because they had a ten foot canoe and paddling over a wave the face of the wave was longer than their entire canoe. I remember thinking "yeah, but the wave is not standing straight up at 90 degrees from the bottom when your canoe was going over it. So what are we measuring?
Oh no, we've all done this one to death...
"Increments of fear" works better for me. Then I know "two feet" means small, "six feet" means solid, and "seven to nine feet" means get off surfline kook.