zangle in parabolic function

how to get correct zangle in current height at parabolic function

use the derivation of your function; it represents the zangle of the function in this specific point

If and only if the height is a function of displacement.

if z = f(x) then ATAN(dz/dx) will represent the angle.

Or take the average between the z of your last point and the z of your current point:

(Zc - Zo)/(Displacement)
Where Zc is current, Zo is the one before.

It really depends on the way you defined your parabola.

i got it thanks.