# how do you check a hydrometer is correct



## red foot marg (Feb 19, 2008)

hi , can anyone tell me how to check if a hydrometer is acurate , i have 3 and they all read different, thanks


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## Graham (Jan 27, 2007)

A hydrometer, or a hygrometer?

The first is used to measure the specific gravity of liquids, the second measures relative humidity, only one letter difference but two very different instruments!

Assuming you mean a hygrometer, as I can't see what you'd want a hydrometer for, testing it is simple using the "damp salt test".

Place a small cup of salt, dampened with water (not wet, just saturated) inside a plastic bag, place the hygrometer, or it's sensor if it has a remote one inside the bag too, seal the bag tightly so no air can get in or out and leave it for 8 hours, after that time if the hygrometer is calibrated correctly it should read exactly 75%.

Some hygrometers can be adjusted, if yours can't then just make a note of how far off the reading is and compensate by that amount whenever you use it.


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## Phasmid_Phriend (Nov 20, 2010)

-stunned silence-

That has to be THE most intelligent, informed and informative reply of the week! And given the fact that it is now 12.01 am on a Sunday, I doubt very much that it will be bettered.
Good work, that chap! :notworthy:


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## red foot marg (Feb 19, 2008)

Graham said:


> A hydrometer, or a hygrometer?
> 
> The first is used to measure the specific gravity of liquids, the second measures relative humidity, only one letter difference but two very different instruments!
> 
> ...


WOW !!, thats great thank you !


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