Shear Force & Bending Moment

One way that these diagrams are drawn:
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Clockwise shear (i.e. when the left-hand side of the beam is being pushed upwards and the right-hand side of the beam, is being pushed downwards) are drawn below the zero line.
Anticlockwise shears are drawn above the zero line.
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Bending moments are always drawn on the tensile side of the beam.
therefore:
Hogging moments are drawn above the line.
Sagging moments are drawn below the line.

We can deduce (to reach an answer or a decision by thinking carefully about the known facts) a simple procedure for ensuring that the shear force diagram always complies(to act according to an order, set of rules or request) with our convention:

START AT THE RIGHT-HAND SIDE OF STRUCTURE AND FOLLOW THE DIRECTION OF EACH FORCE AS YOU WORK TOWARDS THE LEFT-HAND SIDE.