Hello Donald,
I punched in several senarios with the calculator and i believe you are
right.  You don't get the exact figure but close enough.  The board has
random white areas with a random pattern.  For the  multiplying by 3 to
be correct the white areas must be one third of the whole.  The squares
number 15 across and 18 down and are the same size as the sticky boards
i get from the state.  The Dewill Varroa mite detector insert i use at
times has the same size square but is 13 squares down by 11 squares
across (143 total).  I suppose if you blacked out 2/3 of the
squares(approx 95).  Counted the mites on the unblacked squares and (as
Donald said)  multiplied by 3 you would get the same basic result with
less trouble.  Thanks Donald.
I have allways been counting all the mites when i want to be exact.
With the Penn State *varroa board* it would be hard to count the mites
on the black squares. Next spring i will test the Penn State *varroa
board* against the *dewill insert* and see how accurate averaging is.  I
must admit i have pulled inserts with more mites on it than i would care
to count.  The Penn State board has a reusable feature as it is
laminated.
The instructions say:
Cover this board with a thin layer of petroleum jelly;scrape off and
re-coat to reuse.  Clever idea!  Also if you wanted to count all the
mites you could scrape onto a white piece of paper and then count.
Mine was given to me by a fellow beekeeper but i imagine the *varroa
board* is for sale through the Pennsylvania State Bee Lab although i
didn't find info on the boards at their web site.
I have been through many cases of the dewill inserts and cases of ones i
have made with white paper.  Maybe these laminated *varroa boards* would
be a wise investment for the serious beekeeper.
Sincerely,
Bob Harrison

Donald wrote;
>   When you get a total mite number, divide that number by 90.  Now
> multiply the answer by 270 and you have the total number of mites on
> the board.
>
> Would this be the same as multiplying by 3?
>
> Best regards,
>
> Donald Aitken
> Edmonton Alberta Canada