How accurate are Hygrometers?

[bluegeranium]

I am interested to find out the humidity in my house as it seems very dry

I have got one on a digital barometer and two others digital ones with temperature display.

All the temperatures are more or less the same within 1 degree but the humidity varies considerably, on one it says 30% one 36% and the other 43%.

Does this mean that one or more is inaccurate and if so how do I find out? or is humidity measured differently from temperature with a wider range maybe?

thanks