The measure tool determines bond lengths, angles, and dihedrals.
The measure tool allows you to select and assess up to four atoms.
As you click on atoms Avogadro will automatically calculate the distances between atoms in a respective order. For example, the distance between atom 1 and 2 is 1.376 Å (displayed below).
Avogadro will also determine the angle between atoms, if at least three atoms have been selected. The second atom is used as the vertex.
If four atoms are selected, a dihedral angle is determined.
Right clicking the display will reset the atoms previously selected.