Thank you for this reminder. Most of the humidity sensors we like to use (like the Acurite 614) has an accuracy of only +/- 5% RH and the sensors can be subject to long term drift due to the conditions in the cave. Checking with the saturated salt solution is very easy to do, and if you find your sensor is slightly off the mark it's probably drifted a bit and instead of tossing it you can just do a mental "adjustment". Also, if your sensor is reading way off the mark you may want to set it outside the cave in a dryer environment to see if it corrects.