ERROR CALIBRATION ELECTRICAL CONDUCTIVITY??

Hey .. I get a problem when doing calibration with EC sensor, I've followed the calibration according to the instruction. So when I do calibration in 12.88 ms / cm solution, sensor electrical conductivity can only read up to 10 ms / cm and calibration failed. However, when I do the calibration in a solution of 1314 us / cm. Calibration of sensor electrical conductivity is successful.Why did it happen? What sensor electrical conductivity can still be used?
Please help me. Thank you very much.