Cheap and easy scales for measuring high draw weights?

The Lever
The lever is about the simplest of machines, one we're used to
dealing with every day, from can openers to car jacks and millions of
other everyday devices. A lever is used to change the direction of a
force, and to apply Every lever has a fulcrum point, about which
the lever pivots. The two arms of a lever are not equal. A lever lets
you move a heavy weight with a small force, by taking advantage of this
inequality. By applying half the force on the longer side of the lever,
but moving it twice as far, we move the weight on the short side of the
lever. In the lever below, we can move a 1 kilogram weight half a meter
by putting a half kilogram weight on the long arm of the lever, and
letting it push down one meter:




The ratio of the long arm to the short arm tells us the mechanical advantage
of the lever, which is the ratio of work put into the system to work
done. If the long arm is twice as long as the short arm, the ratio is
2:1, and the mechanical advantage is 2. So we could move the weight with
half the force needed if we're willing to move our force twice as far.
This comes in handy when you've got a motor that can apply only so much
force.