The stability of the SeaFETTM Ocean pH sensor is expected to be 0.005 pH units on the timescale of weeks to months (Martz et al. 2010). At minimum, the SeaFETTM should be calibrated yearly.  The body of data collected by the community of SeaFETTM users generally suggests that the stability of the ISFET-based pH measurement offers an improvement by orders of magnitude when compared to glass electrode based pH sensors. Wherever possible the SeaFETTM should be deployed in association with a water sampling program in order to collect water for spectrophotometric pH determination or another external measurement technique.  Additionally, coincident measurement of multiple carbonate system parameters, allow the stability of the SeaFETTM to be assessed.  These approaches have been carried out by a number of researchers over the past several years.