Measure the slopes of the opposite sides. What do you notice? What does this tell about a parallelogram?
Measure the angles of the parallelogram. What do you notice about the about the opposite sides angles of a parallelogram? What do you notice about the adjacent angles? Are all the angles congruent? Do the diagonals bisect the vertex angles?
Measure the sides of the paralellogram. Are all the sides congruent? Are the opposite sides congruent?
Measure the diagonals. Are the diagonals congruent? Do the diagonals bisect each other? Are the diagonals perpendicular to each other?