What kind of scope? I've found the jeweler's loupes aren't good enough, though definitely better than plain eyesight. I'm not sure what the magnification is on my digital scope but it plugs in via USB to the laptop and i can maximize the view to the whole screen it's a lot easier to see. These are some of my scope shots - not all definitive... but I find the more I do it the better I am getting. Things I've noticed:
Preflowers often appear on one side of the plant and not the other (at first)
Preflowers usually not on the lowest nodes.
Always at the newest (but still only one side) but may also be the smallest there. I usually have my best luck about 2-3 nodes down from the top.
You may see preflowers that are not definitive and ones that are on the same plant. If you don't find them at first or you can't tell, keep checking i regularly find multiple preflowers with the scope but can only tell for sure which it is on one preflower.
It's never for sure a female until you see pistils.
It is for sure a male once it forms a claw holding a ball.
Any that I think are probably boys but not sure I put in the dark for a couple of days and the preflowers will extend on a thin stalk and become more ball like if they're male.
This one you can just see the two pistils sticking out of the tip - I wasn't sure if it was a boy at first -- the boys sometimes look like female preflowers that are extra hairy.

Future nuts growing on a stipule (!?)

One of the few real definitive ones

Pretty sure this one ended up female

Most likely a female too

Probably female

Female -- you couldn't tell that with a normal scope

Nuts. Probably wouldn't be able to tell without the digital scope

Could go either way looks female

Nuts

Nuts

Nuts
If I remember right I was gonna call this one a boy and then later found a female preflower with pistils on it. Could be wrong though. It could be both a boy and a girl I'm gonna have to keep an eye on'em just to be sure
