Forbes Marshall offers conductivity standards with different conductivity values, whose stability of ±1% is guaranteed over a life cycle of up to 3 years. These standards can be used several times, on condition that the bottle is not left open (without its lid) for more than 1 hour in total. In order to ensure the accuracy of the conductivity standards, a representative number of bottles from each batch is measured by DFM. The DFM value is recorded on the calibration certificate and on each bottle.