Product review (2 stars): Inaccurate devices from Planet Waves
I purchased two of these to go in the cases of my three acoustic guitars.  I had an oval Planet Waves hygrometer I previously purchased for one of the guitars and decided to get two more for the other guitars.  All three guitars are kept in their cases with a Planet Waves humidifier.  I was noticing what I consider a large variation between the three devices, so I put all the hygrometers in the same place in one guitar case.  There was still a large variation, so I left them side by side on a table top overnight and in the morning checked them again.  The readings were 28%, 31% and 34%.This is a quote from the Planet Waves website about these devices "Accurately displays temperature and humidity levels". The unit with the highest reading is 21% higher than the unit with lowest reading.  I guess in my mind "accurate" is closer to a 5% spread and certainly not larger than a 10% spread.  If the middle reading is the correct reading this does give you a +/- 10% accuracy but only barely. If the middle reading is not the correct one, than there is more than a 10% error on one of the units.  Of course Planet Waves does not list the percent of accuracy of the devices on their website or in their product descriptions...only the quote listed above.  When I had just the one oval hygrometer (which also was the highest reading of the three), I assumed it was giving me accurate data.  Now I don't know which one is correct or closest to correct.