You really don't need a magnifying glass to tell. Sure if you want to see one trichome you do but not over all. Look at it like dust. White dust= cloudy trichs. Amber dust= Amber trichs Hairs can turn anytime after the third or fourth week of flower so it really isnt an accurate measure. Once your buds are ripe you will see the dust getting darker and purple or blue hues on the leaf directly under the buids.
Well, I disagree that you don't need a scope. If you really don't care about what kind of high your product will produce, then don't get a scope.
With a scope, you can actually adjust the high of the finished product by looking closely at the Trichomes. Clear, like diamonds is too soon ... and will produce mostly a head high and possibly some paranoia. Cloudy is just about right if you want a combination of head and body high. Mostly amber ... or all amber, will produce more of a couch-lock high.
Now, go invest the $12 in a Radio Shack 30x scope.
depends on wat kind of person u are! if u wanna get really stoned and lazy u should wait until theyre amberish, if u wanna go with a body/head combination! id go for the couchlock high and wait till theyre amber!