Construction of Parabola via Offset Method:
Given the enclosing rectangle A′ABB′. Divide DA′ into any type of numbers of equal parts or four here and sketch from the division point's perpendiculars parallel to DC, along that the offset distances are to be measured off. The offset varies like the square of their distances from D. As like, as D1 is one fourth of the distance, from A′ to D, 11′ will be (1/4)2 or 1/16 of A′A. Similarly, 2-2′ will be (1/2)2 or ¼ of A′ A and 3-3′ will be 9/16 of A′A. To finish the parabola, lay off the computed offset values along the perpendicular and draw the parabola along with a smooth curve or French curve.
3-3' = (9/16) * A'- A
This method is preferred through civil engineers for laying out parabolic arches and calculating vertical curves for highways.