Instantaneous velocity can be calculated from the position versus time graph. Suppose an object moves from point p1 to point p2. Then its average velocity is given by the slope of the position-time graph. So, if point p2 approaches point p1, and average x-velocity is calculated over shorter time intervals of delta t, then in the limit as delta t tends to zero, the slope of the tangent to the curve at point p1 represents the instantaneous velocity. If the tangent to the position-time curve slopes upward or downward to the right, its slope, x velocity, and motion are positive or negative accordingly. If position as a function of time is known, the instantaneous velocity at any given time can be calculated. Taking the time derivative of the position function, the velocity as a function of time is estimated. Substituting the value of time, the instantaneous velocity can be obtained.