I've tried to look this up and found no real answers so far.

Is there any sort of standard for cutting the chamfer on a thread lead-in?

Say I'm just threading the end of a 1/2" Al rod. The start of the thread
at the end will be jagged and weak. Cutting a 45 (I found 60 does nothing
useful) degree chamfer helps and makes thing far prettier, and for
anything I've done you can just eye-ball this and it really doesn't matter
too much how you do it for my uses.

What's done in the production world for stuff like this where looking
pretty is key? Is there a special angle and distance to cut this chamfer?

Would it be measured as distance into the thread, or the diameter of the
end of the fastner once cut?

Last question- how does one really measure a chamfer anyways? There's no
real surfaces to measure off.