That is still the toughest part of growing for me, and there are no affordable gages, gadgets or gizmos that I know of that will help us with that. Hold a camera or microscope steady enough to take a clear picture is tough so its not like you can run it by by anyone on here. So what I have started doing is making a best guess that its ready for harvest cutting a bud then looking at it through a scope and that kind of works, but there is still the nagging feeling that you should have waited. Why some trichs turn amber before other is probably like Chubby said and it's age.

So I agree that after all the decisions you make growing weed the most important decision is at the end and once you cut its a done deal and you will never know for sure if you did it at the right time