Figure 2
This app represents an interactive version of figure 2.
The horizontal black line reflects the rod of the bismar lever, which has a reference mass m fixed at its right end and an unknown mass M on the left end.
Move the point F defining the position of the fulcrum (point of the rod at which the equilibrium is granted) and see how the mass M changes.
You can move the green point to change the value of the referential mass m.