This paper is aimed at some improvements of the calibration scheme for Moessbauer isomer shifts which, among others, rehabilitate measured rate variations of nuclear electron capture decay as solid and direct sources of electron contact densities. On the ground of an extended block of experimental data and advanced theoretical ideas we come to propose new “best” values for the relative changes ▵R/R of the nuclear charge radius of 119Sn, 125Te, 127I: 1.8 · 10−4, 8.0 · 10−5, –3.4 · 10−4 and 4.3 · 10−4, respectively. The remaining uncertainty is estimated to lie below 10%.