There are lots of diferent opinions about harvesting.
As for myself, i never relied on microscopes to harvest. If you don't need a microscope to harvest a tomato or a banana, you dont need a microscope to harvest weed.
I advice you to use your sensitivity, to develop it. When the plant is ready to harvest it smells like ready, it have an earthy aroma, unlike the grass aroma from imature bud.
The leaves start to die off/yellow.
The bug gains a golden tinge, the calyxes swell, the color most often changes and the hairs all die.
Here is the most awesome thread on harvesting I ever came across:
https://www.rollitup.org/harvesting-curing/210501-zeuss-take-harvesting.html
Also check FDDs thread on Harvesting and Curing forums, the sticky tutorial on harvesting and curing. he has tips on harvesting, incl. pictures.
Of course there are people who will tell you to buy a scope etc, its a matter of personal take.
I myself follow the "instinctive" school... you dont need to be all scientific when you are growing weed, I dont care for the colours shown under a microscope - we have the natural hability to know how to grow and when to harvest stuff, after all, humanity is planting stuff since 20,000 years ago, you know?
I like Argentina very much, BTW.