def dsr_bc(D_eq):
    """
    Beard and Chuang drop shape relationship function.
    Arguments:
        D_eq: Drop volume-equivalent diameter (mm)
    Returns:
        r: The vertical-to-horizontal drop axis ratio. Note: the Scatterer class
        expects horizontal to vertical, so you should pass 1/dsr_bc
    """

    return 1.0048 + 5.7e-04*D_eq - 2.628e-02 * D_eq**2 + \
        3.682e-03*D_eq**3 - 1.677e-04 * D_eq**4