The stability of the scale factor of the LaCoste Romberg gravimeters LCR201 and LCR265 has been studied by analyzing repeated gravity measurements covering a period of five years in a \"relative\" calibration line. Further consideration of the previously used adjustment algorithm showed that it is not necessary to eliminate the additional parameters before the minimization of the trace of the cofactor matrix in order to overcome the singularity problem, since in our model these parameters do not depend on the reference level. Extended reliability tests showed that the network is satisfactory for calibration of the instruments. The results obtained show an almost linear change in the scale factor for both gravimeters, corresponding to 3 x 10-5 per year for the LCR201 and 1 x 10-5 per year for the LCR265. No clear trend was observed for the drift behaviour of the instruments.