I’ve calibrated my pulse pro to another newer device as my one is old. How do you guys calibrate your devices? Mine was way out leading to run a high VPD causing issues since raising my humidity I can finally stop chasing my tail thinking the issue was other things. Just shows you, you are only as good as your calibration 
. I know about the salt trick, putting small amount of water in salt and put inside an air tight container for calibrating humidity. But temp I’d love to hear how other people do this and how often?
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Honestly it all comes down to trust. Pulse publishes +/- on all their products individually and since they don’t make each component themselves it wouldn’t be hard to pop one open and identify which sensors they are using. Long story short they say they use good sensors and I believe them. My method of testing is I put all my sensors inside a bucket in the dark at a consistent temp and covered with no airflow, they are all well within the advertised margin of error of each. Temp usually within 0.5-1.5F and RH within 1-2.5%. Outside a controlled environment I notice heat from the light can effect readings, so ideally it isn’t that close.
The number you see isn’t the experience of the entire plant. I treat trusted devices that show variance as “my plant is in the range of x, and y”. Currently I have a sensor at canopy height and one down towards the middle. Helped me determined when I needed to increase airflow as the heat and humidity diff was increasing.
TL:DR- unless you are seeing numbers wildly outside the published margin of error I’d say you shouldn’t stress. Remember 3% +/- means that if the RH was 70%, that 73% and 67% would both be within the published margin of error(assuming I understand that correctly).