The Rare-RI Ring is a storage ring optimised for Isochronous Mass Spectrometry and operating at the RI Beam Factory in RIKEN. As its name suggests, this device was built to fulfill the demand of high precision mass measurement of rare isotopes which are produced with low yield and have very short half-lives. Unlike other storage rings in operation, the Rare-RI Ring is a cyclotron-like ring and accepts pre-selected rare isotopes event-by-event. This unique operation mode insures achieving high precision mass measurement of the rarest isotopes over a large momentum acceptance. The hurdle of achieving mass measurement at ppm level was overcome using this new mass spectrometer. The new mass of an isotope of palladium with 15 neutrons away from stability emphasized the importance of precision mass measurement in the r-process.