A good hygrometer should be designed for durability, as the environment in which they operate can be rough at times.
Known for their ruggedness and long life, Delmhorst's hygrometers can withstand some proper care from the user (storage, battery, pins, and cleanliness).
However, even the toughest gauges will eventually need to be repaired, or even replaced.
There are several different signs that can indicate if the hygrometer is damaged or not working properly.
However, just because a hygrometer is giving bad readings doesn't necessarily mean it's broken. Many errors can come from environmental factors or error handling.
Some common factors that affect Moisture Meter readings include the following conditions:
Type of material tested
material temperature
The type of wood being tested
low power
If you're sure the bad readings aren't due to the material you're measuring, the battery, or any other factor caused by user error, then you may need to send the meter in for repair or get a replacement.
Below we have provided some telltale signs that you can use to determine if your hygrometer is damaged; hopefully this will help save your wallet and some time waiting for a repair/replacement. 
1. Internal rattles
The hygrometer's internal components should be firmly seated; when you hear a rattling sound while using the device, there is likely a problem. This is usually a good indicator that something is broken or loose in the device.
2. Legibility
Being able to see a clear reading on the display is an important part of the Moisture Meter testing process. As we discussed earlier, sometimes a dead battery can cause the screen backlight to fail or the number fields on a digital display not to work properly.
If you replace the battery with a new, fully charged one and you still get inaccurate readings, it may be something more serious than an internal repair or replacement. In this case, a good option is to contact the manufacturer of the gauge to resolve the issue for a good solution.
3. Not activated
A quick indicator that you should invest in a new hygrometer or that your current hygrometer needs repair is when it is not active. Again, this could be due to a low/dead battery, but if you replace the battery and it still doesn't activate, it could be due to damaged internal components, which may need to be repaired or replaced.
Another common sign of meter failure is an apparently incorrect %MC reading. However, an incorrect reading can be as simple as testing for moisture in the material to which the meter is not calibrated.
For example, two different species of wood with the same actual %MC will show different %MC values when checked with the same gauge. At this point the reading needs to be corrected using the species correction table, or if the Moisture Meter has a built-in species correction, set it to the species you are testing.