pcbondsman (#6190) gave you the essentially
correct answer but less than a better url. (The General
is trying to be "diplomatic" here 'cause he hasn't
forgotten PC's "acquaintance" with some
wiseguys.)
If you go to Yahoo-Finance!'s Home page and scroll
down, immediately below the bottom news headline you'll
see Questions or Comments.
If you click that
on and scroll down, ...and down, .....and down,
you'll eventually get to something that reads as
follows:
Avg Vol
Average Daily Volume is the monthly
average of the cumulative trading volume during the last
three months divided by 22 days. It is updated weekly,
and is provided by Market Guide.
Here's the
link to that Q & C page of Frequently Asked Questions
(FAQ):
http://biz.yahoo.com/f/q.html
Now by the General's reckoning, if you assume that
every month has 22 weekdays (no less trading days, as,
apparently, M-G does), that would mean that a year would
consist of 12 x 22 = 264 days + 52 weeks x 2 weekend
days/week = 104 days = 368 calendar days. It kinda leaves
something to be desired, as the General sees it, to a more
accurate ADV number.
So the obsessive/compulsive
anal-retentive General calc's his ADV on the basis of the actual
number of trading days within the past 3 months' worth
of cumulative trading volume. To each, his own, as
they say.
Fortunately for us, M-G isn't
calc'ing any of NASA's space missions.