Managing humidity is critical to protecting and preserving the condition of your firearms. The LOCKDOWN Hygrometer provides accurate relative humidity readings at a glance. Excessive moisture in a vault or storage area can cause rapid corrosion and pitting on metal surfaces. It is important to monitor and control the relative humidity in your storage area to be sure your guns are properly protected. Mounts easily with included fastener and/or hook & loop. Large easy to read numbers.