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@okPeet Nano Testers: I put together an Excel spreadsheet (download here: http://jmp.sh/vO01Ico ) of VPDs with 3 pages one is based on a 2°F lower leaf temperature compared to the air temperature, another is 4°F lower and the third is 6°F lower. The fahrenheit temperatures in the columns are the air temperature and the VPDs in the chart are calculated on the lower leaf temperature. So to use the charts determine your leaf temperature by using a laser thermal thermometer; take several temps and average them. Lets say your average is 4°F lower than the air temperature. Go to the 4° worksheet, look up the air temperature, slide over to the Humidity % and the intersection is your VPD adjusted for the 4°F lower leaf temperature.
Example: air temp 81°F, leaf Temperature average 77°F, Humidity 60% then VPD = 1.03
Example: air temp 81°F, leaf Temperature average 77°F, Humidity 60% then VPD = 1.03