This paper is devoted to a detailed investigation of a continuous record spanning more than 10 years (1997-2007) of the Strasbourg superconducting gravimeter (SG GWR C026). We show the results from various scale factor experiments using parallel registrations with an absolute gravimeter (AG FG5#206). These results allow us to discuss the time stability of the calibration of the SG. We also superimpose the AG and SG measurements to infer the long-term instrumental drift behavior of the SG but also the seasonal effects present at our station. These long-term effects are discussed in terms of height changes by using collocated GPS measurements (since 1999) and in terms of hydrology (mainly with large scale hydrological models). The collocated GPS height changes help in separating the gravity variation due to the vertical motion of the station from the variation due to the mass redistribution.