Conductivity Standard Solutions and pH Buffers are used for factory calibration of water quality testers. Regular use of these solutions is recommended to ensure specified instrument accuracy. Frequency of conductivity recalibration depends upon use, but once every month should be sufficient for an instrument used daily. pH models, depending upon use, should be recalibrated with pH 7 Buffer every 1-2 weeks, and checked with pH 4 and/or 10 Buffers at similar intervals.