The graph obtained was a velocity time graph. The gradient of this line should tell us about the acceleration of the ball bearing.
Galileo realised that the only force acting on the ball was gravity. This force only acted in the y direction.
Most of us obtained a straight line-a line with constant gradient implying that the acceleration was constant. (A=g sin (angle of the ramp)
If a scatter graph is drawn, a regression line tells us if the data is reliable, that is does it agree with a straight line (y=mx + b). A low correlation coefficient, close to zero, implies the data is not reliable. If the coefficient is close to 1, the data is reliable.