Ac infinity vpd thermometer questions

So I've had the vpd thermometer for a while and I'm trying to calibrate my ac infinity controller 69+. My question is when you subtract the leaf temperature - room temperature, can the answer be in the negative numbers? The reason I wanna know is it lowerd the VPD drastically and idk if the calibration is off.


Any helpvis greatly appreciated

RTFM
page 13

Determine the leaf offset by taking your leaf temperaturereading and subtracting your room temperature reading from it.Note that this can result in a negative number. Round the leafoffset to the nearest whole number and enter this figure intoyour VPD-enabled device under its settings.

solakani said:

RTFM
page 13

Click to expand...

"RTFM" -
Sounds like someone who's worked in tech support.

What @solakani said.

The leaf temperature offset will be a negative number because the leaf surface is cooled when water evaporates from the leaf during transpiration. There's a very thin layer on the leaf surface where the temperature is lower and that helps cool the plant.

Strange that this came up. I just sent a PM to someone about 5 minutes ago:

"Leaf temps will usually be -1°C vs ambient but wind speed is an issue. I was at -5°F (-2C?) for most of my last grow. I was really reluctant to use that number but I replaced my old el cheap IR gun with a new one from AC Infinity (only $25 but a much better product) and, yup, it was pretty chilly under the canopy."

-2°F is a decent ballpark number.

Delps8 said:

"RTFM" -
Sounds like someone who's worked in tech support.

Click to expand...

No. I have never worked in India.

solakani said:

No. I have never worked in India.

Click to expand...

Yeh, I get it.

30+ years in software, including three years of Apple, so I've been around for a lot of changes. Simple fact is that Americans are expensive. "You can have it good, you can have it soon, you can have it cheap—pick two."