can't see trichomes on calyxes...
trichomes
density
pistil coloration/retraction
even if unsure now, if you track those three it'll become more apparent each time when you want to harvest. none are perfect indicators, but using all three will keep you more consistent... if oyu are not sure if you prefer early or later harvest, this helps figure that out too... you will more easily pick out an early or late based on these 3 observable factors. experiment... maybe you even want some with a ton of degrdation for nightime smoke and some that isn't going to put you to sleep? all personal preference at that point... trial and error to learn what you like.