One great way to test if a helmet fits correctly is the twist test. Once the helmet is on, fasten the chin strap and make certain everything is snug. Hold the helmet and try to roll it off the back of the head. If the skin on the forehead is being moved then the helmet fits properly. Also, twisting the helmet side-to-side should cause the head to turn, and not allow the helmet to twist on the head. If the helmet passes these simple requirements then you have found a properly fitting helmet. Many companies will also have a fine tuning system to help compensate for small changes in the padding. One such system is known as In-Form; this system originated in bicycle helmets and utilizes a floating carriage at the back of the head. A dial or slide lock allows the user to loosen or tighten the carriage to fine tune the fit of the helmet.