How to Understand the Conductivity Accuracy ±1% F.S.?

When your Apera conductivity meter specifies an accuracy of ±1% F.S. (full scale), it means that the meter’s reading can deviate from the true value by up to 1% of the meter’s maximum measurable value (the full-scale value) rather than 1% of the reading at the moment. 

Apera conductivity meters’ range is divided into several full-scale values. For example, the EC9500 Conductivity Meter’s range is 0 to 2000 mS/cm divided into six full scales ––  

Say, if you get a reading of 1400 µS/cm, it falls into the 200 to 1999.9 µS/cm scale, in which the full scale is 2000 µS/cm. So, the instrument accuracy in that full scale is ±1%*2000 µS/cm= ±20 µS/cm.  

Meanwhile, the ±1% F.S accuracy is only the error from the instrumentation alone. Taking the potential error from the conductivity sensor and the calibration solutions into consideration, a more practical total accuracy of the reading should be around ±1.5% F.S, which in this case is ±1.5%*2000 µS/cm= ±30µS/cm.