def delSomeKeywords(hdr):
    """Delete exposure-specific keywords.

    Parameters
    ----------
    hdr: pyfits Header object
        Extension header to be modified
    """
    for key in ['shift1a', 'shift1b', 'shift1c', 'shift2a', 'shift2b',
        'shift2c', 'dpixel1a', 'dpixel1b', 'dpixel1c']:
        if key in hdr:
            del hdr[key]
