Oasis" OH-5 Plus + instrument humidifier keeps your guitar, or any other wooden instrument, in prime condition with the correct level of humidity. It"s important to keep the relative humidity above 40% to prevent the instrument from cracking. With this comprehensive set, you can measure humidity levels and administer the instrument humidifier. It includes the OH-5 Plus+ Humidifier and OH-2 Digital Hygrometer with clip for attaching near the instrument or in the case.Oasis OH-5 Plus+ HumidifierWhile the original Blue Oasis provides sufficient humidity in many environments, it is not effective everywhere. The humidity demands of the desert, mountain states or frigid north exceed the humidification capacity of the device. For this reason, Oasis developed the Oasis Plus+ humidifier. The Plus+ is the same size and shape as the original blue Oasis, but is made of a different material that provides 50% more humidity output.Because the Oasis Plus+ HumidifierPlus+ is the same size as the original Blue Oasis and it has 50% greater humidity output, it will be necessary to refill the Oasis Plus+ more frequently than the original Blue Oasis.If one is using a hygrometer, Oasis recommends that the Oasis Plus+ be used when the room humidity is below 25%. The original Blue Oasis should be used when the surrounding room humidity is between 25-40%. Above, 40%, you should not be using a humidifier.It is important to also to monitor the humidity inside your instrument case. Case size, design, material and other factors will impact the humidity permeability of each case. While general rules are helpful, a good hygrometer located inside the instrument case will give you the best information regarding proper humidification requirements.OH-2 Digital Hygrometer w/clipThe Oasis Digital Hygrometer accurately measures relative humidity and can help you decide when to use your Oasis Guitar Humidifier. Because relative humidity varies greatly, even inside your home, we recommend that you keep you