There’s a lot of devices that calculate vdp without leaf temp, not saying it’s as accurate without using the whole formula, but they do. I know the controller 69 does also.
VPD is always calculated with a leaf temp in the equation.
If the calculator only uses air temp & RH, then still it is always fixing the leaf temp to match the air temp in the math, & you just don’t see it. It gives you the ‘Room VPD’. It would be the same as using a zero-offset chart. Most controllers are set to some default offset (probably zero) & it is the users job to find out what the offset actually is, & then update the controller with the actual offset.
The 69 pro allows you to set your leaft temp difference in the settings. It defaults to 0°. I’m still new but I use a combo of my humidifier and ACI inline to control my environment. You can see at the bottom my fan kicks up @64% to help keep it in check. Just have to fine tune it. I adjust my humidifier down just before lights out by 10%. My humidifier has a min-max setting in 5% incr. With 3 different mist settings. And it was off amazon.
What type humidifier are you using?
On the 69 you can adjust for leaf temp…
Even without accounting for leaf… You vpd should be easier to control.
What size tent? Room?
My lung room last winter formed frost on my basement walls… And had moisture form in my exhaust tubes… That sucked…
I stop now December through to March… Just getting ready for planting next week.
My de-humid is out on loan and returns soon.
Dec 26 King Tide flooded a friend’s house, 1st floor under two feet of water.
He said it been working like a beast.
going on 8 years, now, mostly 24x7 for 5years in Japan.
These would remove moisture, eliminating frost and moisture, and give you water for grow.
Winter is my best time to grow, heat shouldn’t be a too much issue, just not enough.
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I have a 70 pint dehumidifier in my lung room… I should use the water… But it goes down the drain.
My dehumid adds almost 5-10 degrees increased temp (summer).
Lung room drafty with windows open or closed.
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My lung room…is closed all the time… Bad state for growing here.
You’ll drive yourself crazy chasing VPD numbers. 50-60% RH in Veg and 45-50% in flower with temps 68-80 and your plants will flourish 
I’m sure it drives plenty people nuts, I like the challenge
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I’ve bought just about any kind of humidifier on Amazon. They all suck! Ultrasonic, unless using distilled and even then throws dust everywhere! Any “smart” humidifier coming from China will more than likely have a junk hygrometer, tried one of those. Then evaporatives are a joke with tiny little paper filters. I know there’s a few hidden products that may work out there, because someone is going to feel the need to chime in, but mine brings more to the table than I had imagined and was my missing link for achieving that stable environment in striving towards.
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2.5x2.5x5. 2 plants in 5gal maxes it out with fans and humidifier. Might be able to run 3 by moving the humidifier out, but that’s unsightly when you could walk in and out without knowing I’m growing. Super stealth!
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Very ingenious… Hook it up to an inkbird humidity controller… Set the controller to a rh you want then add high and low limits… It will turn in only when necessary within the range you set. On the dehumidifier side of it add a fan to bring in drier air.
Same for heat… Other than heat from light… An oil filled radiator heater and a fan blowing cooler air into the bottom vent when needed.
My temps and humidity stay stable.
I use this for my humidifier:
I use distilled as even RO leaves residue.
I just bought an RO buddy 4 filter… 3 used for RO… All four used for distilled.
I was spending over $100/grow on RO and distilled water.
Our well water is hard to deal with plants with.
Definitely no option for leaf temp on the Govee hygrometer.
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@marthajeep The charts are better… One online is in excel… You put in your numbers it’ll give you a heat chart based on your data. I use govee as well… But mine don’t have vpd.
I hear you on the buddy. Got one for my saltwater tank before I grew. What a waste! Never thought it be so expensive. After retiring the tank I bypassed the ro and just used the sediment and carbon to rig up to a gravity feed dog bowl. Used a mini toilet plunger. Now the dog has constant fresh filtered water and I’m not wasting as much pushing water through a membrane
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After more digging, this is what I think. It is possible to calculate vpd without leaf temperature, as it is calculated based on the difference between the saturation vapor pressure (which depends on air temperature) and the actual vapor pressure (which depends on both air temperature and relative humidity). However, leaf temperature can be used to estimate the actual vapor pressure more accurately, which can improve the accuracy of the vpd calculation.But it’s recommended to use leaf temperature data whenever possible for more accurate results.
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You know mine didn’t have vpd until I just recently I noticed. Also has dew point, but I think it popped up after a firmware update or battery change. I was surprised when I first saw it