def _calculate_missing_corrections(corrections_dict):
    """Fill in odd wavelength values in corrections dictionary.
    
    ISS provides corrections for even wavelengths (i.e. 250 nm, 252 nm,
    etc.) For a given dictionary of corrections compiled by
    _construct_corrections_dict(), this function calculates corrections for odd
    wavelengths by averaging the adjacent two values.

    Return a dictionary with integer wavelengths as keys and corrections
    as values.

    Intensity data should be divided by the correction value corresponding
    to the wavelength at which it was collected.
    """

    expanded_dict = {}

    for i in range(250, 901):
        if i in corrections_dict.keys():
            expanded_dict.update({i: corrections_dict[i]})
        else:
            expanded_dict.update(
                {i: (corrections_dict[i - 1] + corrections_dict[i + 1]) / 2}
            )

    return expanded_dict