The screen formula in SIM is
dh = kirschmer_shape_factor (bar_width / bar_spacing)(4.0/3.0) sin(angle) vus2 / 2 g

Where,dh is headloss (m)kirschmer_shape_factor is an empirical factor that depends on bar shapebar_width is the width of each bar (m)bar_spacing is the space between each bar (m)angle is the angle of the screen wrt horizontalvus is the approach (u/s) velocity (m/s)

One thing to note, however, is that the angle in the ICM UI is measured wrt the vertical (they may not have taken this into account).

So, what we call the compound discharge coefficient (ccdw) for the screen is

ccdw = width sqrt(2 g) / sqrt(alpha)
where alpha = kirschmer_shape_factor (bar_width / bar_spacing)**(4.0/3.0) sin(angle)

For a standard WEIR

ccdw = Cd width sqrt(g)

Thus Cd = sqrt(2) / sqrt(alpha)