I too have seen many autos that amber up very little. I have been going by the leaf yellowing method, but I am beginning to think I may be letting things go a little too long. The vast majority of my grows go over 100 days, and many have gone 120 days. I do alot of LST, and think that it may be the cause of my long grow periods. Well worth the longer grow time with all the extra yield from the LST. I think that by letting them go till leaves yellow, that I am losing that good strong smell after harvest. The potency is always good, just not much smell. I do check trichomes with a digital microscope on the strains that do amber, I go for a 20-30 percent amber. But then again, I am sure everybody's estimate of amber percentage would be different even if everyone inspected the same bud. I've seen pics that people are calling 20%, that I would call a few random amber. Most of the time, I don't need any magnification to tell when things are clouding up, I can see it naked eye when the buds suddenly take on a noticeable "glow". This next grow I am going to start water only when I notice the glow, and harvest 2 weeks after that, yellow leaves or no yellow leaves. Just want to see if it makes any differances in the smell department.