Expert: James Yee - 5/10/2009

Question
I have been reading that it is recommended to use digital hydrometers, and i
purchased one.  It has an adjustment feature and its confusing me how to set
it up.  The device says for best results use their one step calibration kit (by
humidipak) but it says its pre done.  The directions state to place the
hygrometer inside the bag (i don't know bag) and allow the bag to sit for 24
hours at room temperature 65 to 75 F.  It says the hygrometer should read
+ - .3% of the RH level stated above (75%).  It says to note the difference if
any of the reading and 75%, and this number will have to be adjusted.  What
is the number 75% and do they mean to use a regular zip lock bag.  How
would you calibrate a hygrometer with an adjustment feature?  Thank you.

Answer
Hi Michael,

Digital hygrometers are usually factory-calibrated and extremely accurate.  Just to be sure, you should test your hygrometer for accuracy with a salt test but it may not be necessary to calibrate it as it could already be accurate.

To salt test your hygrometer, take a small plastic bottle cap or small dish and add one teaspoon of regular salt.  Add a few drops of distilled water to the salt and mix it up so that the salt mixture has a crumbly texture.  Next, take this mixture and place it in a Ziploc bag.  Add your hygrometer to the bag but do not let the salt mixture touch your hygrometer at all.  (If salt touches the hygrometer, it could damage the electronic components.)  Now, seal the bag and let your hygrometer sit for at least 12 hours.

The salt mixture is guaranteed to generate 75% humidity so if after 12 hours, the hygrometer does not read 75% humidity, you know it is not accurate.  If the hygrometer reading is higher or lower than 75%, adjust the hygrometer so that it now reads 75%.  Your hygrometer is now properly calibrated and ready to be used in your humidor.

As for using the adjustment feature, every hygrometer is different so you should check the instruction manual that came with your hygrometer as it should explain how to calibrate it.

Hopes this answers your question. As always, if you have any more questions, please feel free to just ask and I will be happy to help.

Regards,
James