Principle

On the one hand, the students should investigate the effect of
two forces acting in the same direction on a mass piece; on the
other hand, the effect of two forces acting in opposite directions
on it.

From the comparison of the two measured force with the given
weight (force) they should deduce the relationship among the 3
forces.

The term "(slotted) weight" is incorrect since we are dealing
with a mass which becomes a weight (in reality "a weight-force")
under the influence of the earth’s gravity. The term "mass piece"
used here is better.