HOBOnet TEROS 11 and TEROS 12 soil moisture sensors come calibrated for most soil types. However, for soil types with high sand or salt content, the standard calibration may not be accurate. In such cases, soil-specific calibration should be used.
To determine the soil-specific calibration formula, please refer to: https://www.onsetcomp.com/support/tech-notes/calibrating-ech2o-soil-moisture-sensors-application-note
Please note too that because the HOBOnet TEROS 21 sensor measures soil water potential, it does not require soil-specific calibration.