  Signs of the different contributions to the isotope shift of an atomic line
are discussed in details to clarify some confusing differences between the
electronic parameters calculated with RIS (Naz\'e et al. Comput. Phys. Commun.
184 (2013) 2187 ; Ekman et al. Comput. Phys. Commun. 235 (2019) 433) and those
appearing in other commonly used expressions.
