def mean_residue_ellipticity(phi, n, c, l):
    """
    Calculate mean residue ellipticity (millideg cm2 / decimol) from
    ellipticity (mdeg)

    Args:
        phi (float): a ellipticity (milli deg)
        n (int): the number of residues
        c (float): the molar concentration of the polymer (mol/L)
        l (float): the length of the cuvette (cm)

    Returns:
        a mean residue ellipticity (deg cm2 decimol^{-1} residue^{-1})
    """
    return phi / (10 * l * n * c)