Well let us look at the link above-
I follow that link I see calculations where the temp and altitude are the same. This was the way I understood it before the link I just did. Note: vpd above the leaf which requires leaf offset Room altitude and temp are the same on both calculations and therefor irrelevant
Edit to note- should likely be vapor-pressure in each and the difference in vapor pressure in each calculation is the vpd
I don’t see altitude mentioned at all in these calculations, but typically I assume it’s done at sea level. That still doesn’t help much as far as precision. As far as it being irrelevant… it’s relevant if we’re trying to precisely calculate VPD, which is what the thread was about in the first place. OP asked if other people were precisely calculating VPD and how to do it if so, and we’ve all been explaining how we do it. I’m not saying I precisely calculate my VPD or advocating it as the best way to do things. I’m saying I don’t and just follow the damn charts roughly, because the charts are all inaccurate anyway. For example; the calculator you linked has 75F/60% listed as 1.18 VPD and 70F/60% listed as 0.73. Grouchy’s chart lists them at 1.02 and 0.85, whereas mine lists them at 0.87 and 0.73 (assuming +5F baked in). The differentials between the room and leaf VPD change according to which chart you use. Great, isn’t it?
the vpd as I understand it is calculated for the room(tent) and for the leaf. Both of which are in the same room and at the same ambient temp and pressure. Edit to add- the difference is due to the transpiration which cools the leaf varying the pressure.
Clearly they’re in the same room and at the same pressure. I wasn’t questioning that. I’m questioning how the details of these charts are different for each one. If pressure doesn’t make a difference in the calculation, why does your calculator say 5F between the leaf and room makes for a differential of 0.45 kPa while Grouchy’s says it’s a differential of 0.17 kPa and mine says it’s a differential of 0.14 kPa?
5 degrees doesn’t explain all the differences. Would think leaf shape and wind velocity in these algorithms somewhere. Not sure how accurate the charts are or what constants or even decimal places are chosen. personally 0.03 is negligible… 0.45 otoh…