You have 12 bowling balls and 1 huge scale, the old school style where
you have two platforms which you can place objects on either side(as
many as you want).
One of the 12 balls is either heavier or lighter than the rest.  In 3
uses of the scale determine which ball is not the same weight as the
others and whether it is lighter or heavier.

mpower -- 

The answer to this question is extremely difficult to explain in
"plain text" because of the different processes that have to be
followed depending on the results of the first weighing.

So, I spent my research time looking for the most comprehensible
online explanation, and I think I have found it.  The site linked
below cleverly allows the solver to follow up each possible result of
the first weighing (scales balance, left side falls, right side falls)
by linking to a new page that explains the appropriate second weighing
procedure for each case.  Then a new link is supplied to provide the
appropriate third weighing procedure for each result of the second
weighing.

It really isn't as hard as it sounds to follow the logic at this
interesting site, so here's the link:

Mazes: Scale Puzzle 301
http://www.mazes.com/scales/Scale301.html

If you have any problems, let me know, and I will help you through it.


Search Strategy:

The following Google search comes up with lots of sites that include
versions of this puzzles., including the one described above:

scale 12 OR twelve 3 OR three heavier lighter
://www.google.com/search?sourceid=navclient&ie=UTF-8&q=scale+12+OR+twelve+3+OR+three+heavier+lighter


I am confident that this is what you are looking for, and I was glad
to be able to provide you with the answer promptly.  As I said above,
if anything is unclear, please ask for clarification before rating the
answer.


markj-ga