Note that the highest point is A, the lowest point is B, and the vertex is C. Then A, B and C can form a triangle, and the vertical line from the edge of A to BC is D. Because the swing angle is 60, ∠ ACB =1/2 * 60 = 30.

Because the length of pendulum chain is 4m, AC = 1/2 * 4 = 2m, BC = 2m.

And CD = ACCOS 30 = 2 * (root number 3)/2= root number 3.

So BD=BC-CD=2- root number 3

That is to say, the difference between the height of the swing to the highest position and the height of the swing to the lowest position is (root 3 of 2) meters.