Simply soak in water and slip the flexible tube (color may vary) through the F-hole of your instrument. Note: this will not fit into all fractional cello f-holes. Tube diameter is 15.5 mm at its thickest. Its easy to monitor with the included humidity indicator card!Why use a humidifier?The winter months ahead will bring with them colder and drier air which can be dangerous for instruments and bows. Wood absorbs and releases moisture as humidity levels change in the surrounding air. Instruments are, of course, made of wood. Dry air causes wood to release moisture which causes it to shrink and/or shift ever so slightly which for your instrument can lead to cracks and expensive repair bills. Of course most instruments will not crack, but as your instrument dries out, its tone will change, and seldom does it change for the better! Bow horsehair shrinks in dry air which can impair sound quality, or cause the bow to warp, or could even result in a disastrous bow tip break. A good phrase that comes to mind is: "An ounce of prevention is worth a pound of cure." Purchasing a relatively inexpensive humidifier will protect your investment and you to sound your best.