i probably have the same. mostgarden centers of big shopping boxes have it.
you need to calibrate your hygrometer before using it.
you can google how to do that, there's also a thread here about that.
involves mixing salt and water in a container and putting same inside a ziploc bag together with your hygrometer.
hygrometer should read 75%, if not, either adjust it or take note of the difference and always remember that when getting a reading.
it is very important to have the desired level of humidity during the incubation and hatching process.