Relative humidity is the amount of moisture in the air at that point of time. Your surrounding rh might be whatever, but inside the dry cabinet, if it says 45%, it means 45%. If your country is very humid, however, it'll just be harder to get your desired setting as the dehumidifier has to work a lot harder.
RH ( Relative Humidity) , is the amount of water vapor in the air, relative to the maximum capacity that the air would take under the given condition ( temperature / pressure) That means, the real amount of water in the air different when temperature or the pressure changes, also the RH Value stays the same. Just as an example for better understanding. At a stable given barometric pressure, 40%RH air contains around 9g/m3 water at 25 degrees celsius, but only around 5g/m3 at 20 degree celsius. If the temperature or the pressure changes, these values of g/m3 ( absolute humidity) also change. However, as temperature and pressure always change in our world, measuring humidity in absolute values is impractical. Therefore , we measure at the value, relative to the maximum amount of water vapor the air can take.