You can use the parameters on this tab to modify the beam length or to create a diagonal cut.
Reference
Defines the shortening (or lengthening) size. A positive value trims the beam and a negative value extends the beam.
Y
Defines the rotation angle around the main Y-axis of the beam.
Z
Defines the rotation angle around the main Z-axis of the beam.
Length
Defines the length increment (grid jump) when modifying the shortening position using the grip points.