Check those trichomes brother ! You want a 30x or more loupe should only set you back a couple of bucks or a pocket microscope, mine cost about 15USD, it has a LED light in it that makes viewing a bit easier and does 60x to 120x.
I'm no expert at using this method to determine best time to harvest, I've only used it once myself but I harvested at mostly milky with a hint of amber about 5% and was happy with what I got, I like a strong head high.
Do a little googling there is plenty of information on the subject.
Before the days of checking trichomes we would just say it's ready when 75%ish of the hairs we're coloured, not as scientific but works alright.
Again do a little googling, these numbers are off the top of my head ....