Question
What are the units used on the soil moisture graphs?
Answer
Observant uses an arbitrary 'Moisture Units' (MU) to monitor changes in moisture levels.
Overview
Observant’s goal is to enhance your ability to use soil-moisture-monitoring technology to develop consistently-wise irrigation decisions.
An annoying complication associated with soil-moisture probes and sensors is the calibration needed to convert their raw data into units of measure that are considered meaningful, such as the percentage of Volumetric Soil Moisture (VSM %). Because proper soil testing and sensor calibration can be both tedious and prone to error, the accuracy of the data produced may be questionable despite the time and expense expended to produce it.
What truly matters to most of us is our ability to keep soil moisture levels within a particular range (typically between a given field's water holding capacity and a moisture level that incurs stress on the crop). Observant’s approach, therefore, shifts the focus from reliance on calibrated, absolute values to a judicious use of raw sensor data — expressed in arbitrary 'Moisture Units' (MU) — to monitor changes in moisture levels.
Using the Observant Global™ software platform, you can maintain the water content of your crops' root zones within predefined boundaries (the green zone in the diagram below). 
You will be able to reduce the likelihood of having a crop stressed by a moisture deficit and avoid excess expenditure of your water resources. Observing the trends of moisture data in your crop's root zone will support increasingly effective and efficient irrigation decisions.
Relevant Articles
Please refer to the following articles for further reading: