The pH and Temperature Pen requires pH4, pH7, and pH10 buffer solutions for wet calibration and pH sensor storage solution for proper storage. 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. pH Sensor Storage Solution is recommended for keeping the pH sensor wet.