AVHRR clear-sky brightness temperatures (BTs) over ocean and derived sea surface temperatures (SSTs) are produced at NOAA from several polar and geostationary sensors, including AVHRRs onboard US NOAA and European MetOp satellites. Analyses in the Monitoring of IR Clear-sky Radiances over Oceans for SST system (MICROS; www.star.nesdis.noaa.gov/sod/sst/micros/) suggest that artifacts in SSTs are strongly linked to anomalies in BTs. To attribute anomalous BTs to calibration information reported on L1b data, NOAA established another online system, Sensor Stability for SST (3S; www.star.nesdis.noaa.gov/sod/sst/3s/). The 3S monitors orbital statistics of calibration gains and offsets in AVHRR SST bands, along with the onboard measurements of blackbody temperature, blackbody view count (BC) and space view count (SC), from which the gain and offset are calculated. Sun and moon geometry configuration, which may affect the BC and SC, is also monitored, as well as the length of the “satellite night” (part of the orbit, when the satellite is in the Earth shadow and AVHRR calibration is presumably more accurate). Currently, the 3S displays time series of all statistics for NOAA-15 to -19, MetOp-A and -B. This presentation describes the 3S system.