When picking up a cooler, I also picked up 2 of these hygrometers from Walmart for $9 each. After picking them up, I noticed they seemed to fluctuate wildly. They would jump 5% either way after sitting on my counter for an hour. Same in a glass topped humi I could watch. Same during a salt test!
I then decided to look for reviews (yeah, kinda backwards). All I could find were reviews on the Acurite 00613 model from a few years ago. Besides the case and the display screen setup (same data, just different display mapping), I don't know if there is anything else different between the two. I don't know which is older/newer, but here is an image of the 325 and 613 for reference...
Acurite 00325
Acurite 613
All (or most) of the reviews for the 613 similarly complained about the inaccuracy. I did find one reviewer who claimed to have drilled holes in the back of his to increase air flow through the device and he then was happy with it. Looking at my 325, I noticed that his comments about lack of airflow into the sensor applied to mine as well. On the back, there were indentations that I believe were meant to allow air flow, but most had no opening at all and a few had a tiny pin prick (visible when holding the back of the case up to a light after separating from the main unit by 4 small screws).
Since I already had them, I figured what the heck. I screwed the backplate back on and used a small flat head screwdriver to gently punch in the indentations. They were pretty easy to push in without too much force, except for the top two on each side. These are closest to the circuit board, so I decided not to force them. I then did the salt test again with both units in the same bag. Within 4 hours one was reading 74% and the other 75%. At 5 hours they both read 75%. I checked them hourly on average until about 12 hours total time with no change. After about 8 hours additional they still both read 75%. I waited 4 more hours with no deviations (checked hourly).
After the quick fix, I am super happy with these hygros. They are quite a bit larger than the puck style units, so I would not recommend them for a small humi (work great in my coolidor). The fact that they show a high and low for the past 24 hours is nice to have though, especially if you're worried about fluctuations. I was worried about temps, but glad to see a 68 low and 70 high! They're also pretty cheap. They are not adjustable, which had me kind of worried, but now that there readings have stabilized I have no complaints.
