Uncertainty analysis for the Twomey parameter (regression slope droplet concentration, Nd vs. cloud condensation nuclei concentration, Nccn) as a function of errors in both input quantities (cf. Hasekamp et al. Nature Comm 2019 doi 10.1038/s41467-019-13372-2) for use in Quaas et al. (ACP 2020; doi 10.5194/acp-2020-279)