Pressure chamber readings are the current gold standard to determine plant water status. Unfortunately the measurements often depend on the operator (i.e. different users get different results) and the high pressure instrument is a safety hazard. The logistics of the pressure chamber are also painful, and require visiting remote fields with a heavy instrument to take measurements during the hottest part of the day. With these drawbacks, most research can maybe get one measurement a week of uncertain accuracy. You need accurate, automated measurements.

Stem psychrometers have existed for many years now and are a well-known tool to measure stem water potential in a variety of crops. The instrument has a well-understood mechanism of measurement, and can provide accurate measurements when installed and handled correctly. Unfortunately, this instrument is fragile and requires experienced hands for correct installation. Even when installed correctly, the instrument will usually fail after days to weeks due to intrusion of the plant exudates into the measurement chamber, or loss of contact of the thermocouple pair. The instrument further requires expensive electronic equipment to read the microvolt signals.You need an instrument that is accurate for the long run.

​Sap flow meters measure the flux of water through the plant vascular system (xylem), which is difficult to interpret because there is no 'gold standard'. Each tree will have different sap flow readings depending on its own particular trunk structure and this unfortunately means that sap flow needs to be calibrated for each individual plant. In other words, two trees with the same sap flow measurement could have wildly different water status.