A VPD of 1.3 would be, perhaps, early flower.
There are two pieces to the Pulse VPD puzzle - the stage of growth and the leaf surface temperature ("LST")
Recommended VPD's are 0.8 for seedling, 1.0 for veg, and 1.5 for flower. Some growers like to gradually raise VPD when flower starts, going from 1.2 to 1.5 so maybe that's where 1.3 is coming from.
LST is an important part of VPD because it drives the "deficit" part of VPD, that is the difference in vapor pressure within the leaf vs the vapor pressure outside the leaf. The vapor pressure outside the leaf is a function of the temperature and the humidity - if is really hot and dry, there will be a big deficit and lots of transpiration. LST is used for the "offset" - the difference between the leaves in the canopy and the ambient temperature in the tent//grow environment.
Grab an IR thermometer and sample the temperature of leaves in the canopy. If the ambient temp is 80 and the LST is 78, you've got a -2 offset. Click on the "Settings" icon ("Environment", "Spectrum", and "Settings") and scroll down until you see the place to enter the LST. Once you've entered that, hit "save" or "accept" and the Pulse will update the data based on the LST that you've entered.
The Pulse site is well worth checking out. Read through the docs and sign up for the newsletter. Pete is the programmer for their products and is their tech support guy. Very laid back and eager to help. There's a forum there, too, so you can ask/answer questions. I add my tuppence there as "OC_Grower".
I bought a PulseOne last year and it's the brains of my grow. I use Bugbee's "nine cardinal parameters" as a guide for my growing processes. About the only items that are truly "variables" are temp and RH* and the Pulse allows me to get the temperature and RH spot on with almost zero effort.
*OK, there are thrip infestations, hot and cold temperatures because my grow is in an unheated garage, power outages, and being a dumbshit who says "Nah, I don't need a trellis" but other than those things that make it a goat rope that, it's smooth sailing.