# Agriculture Sensor FAQGeneral Sensor FAQ:

 Question Answer What is GWC and how is it different than VWC? Gravitational Water Content (GWC) is the mass of water per mass of dry soil. Just like Volumetric Water Content (VWC), it is another way of determining how wet your soil is. There are no technical differences between GWC and VWC, as they both calculate the same result (ie. "The soil is wet by X amount"). The only difference between GWC and VWC is how the result is presented. GWC presents the mass of water in terms of grams (g) and VWC presents a percentage (%) of how wet your soil is. How do I interpret GWC? As GWC represents only the mass of water per mass of dry soil, it is not possible to interpret the measurement as a percentage. Therefore, you can assume that any value between "Dry" and "Wet" has a degree of water content in it. Values exceeding the "Wet" threshold can be interpreted as more "wet." How do I convert GWC to VWC? See the following formula:VWC = (GWC * soil density) / (water density) Important note for customers using fertilizers/additives: When converting from GWC to VWC, you might find the results to be inaccurate. This inaccuracy may come from any additional fertilizers/additives applied to the soil.As the Agriculture Sensor was only tested with regular water/soil, it may not be able to accurately match the VWC conversion. How do I convert the readings for soil moisture into GWC? Input 1 readings are a frequency presented in kHz.  Please refer to the table below for a conversion from this frequency to GWC (gravimetric water content): How do I convert the readings for soil temperature into °C? The readings from register 0x 02 02 (Input 2) are a voltage, in mV.  The premise is, when the voltage reading goes up, the soil temperature is dropping. The formula used to perform the conversion is: soiltemp = -32.46*LN(V)+236.36.  Refer to the following table for a quick look-up of the conversion:      How do I convert the readings from the Thermistor and Watermark into Soil Water Tension? Watermark 1 & 2 will provide frequency readings.  A reading of soil temperature from the thermistor will also be taken into account when calculating the final kPa value of soil water tension, for increased accuracy. Final kPa of soil water tension is calculated by the following steps:           1.  Obtain a reading of the frequency from Watermarks 1 or 2 or both.  These are registers 0x 05 04 and 0x 06 04 respectively.  Table 2-4 below can be used for conversion of the frequencies read from the Watermarks to get an initial kPa value.  From Table 2-4, use the column on the right to find the appropriate range that the reading from the Watermarks fits into.  Then use the formula directly to the left (from the left column) to calculate the kPa of soil water tension. 2.  Obtain a reading from input 3 or 4 or both.  These are registers 0x 03 02, 0x 04 02 respectively.  Use the equation below to calculate a temperature from the mV reading.             Temp = -31.96ln(x)+213.25             x = mV reading from input 3 or 4 This calculation represents the soil temperature.          3.  Perform this next step only if the soil temperature varies from 24°C.  Using the initial kPa value calculated in step #1, and the soil temperature calculated in step #2, calculate a ‘temperature adjusted’ kPa of soil water tension by using this formula: 