What is a platform balance and how is it used?
A platform balance is an instrument to weigh things.
From Answers.com (see link to the left):
The platform balance is a form of equal-arm balance in which two
flat platforms are attached to the top side of the beam, one at
each end. Such a balance has a rider, or weight, mounted on a bar
that has a calibrated scale, is parallel to the beam, and connects
the supports of the two platforms. This rider is moved along the
bar, its edge marking decimal fractions of the unit weight.
See the Related Questions to the left for more information
about how to weigh a sample on a balance.