Below are some guidelines to follow when fitting a Comfort Select mask. Landmarks a.) Sides of nostrils b.) Bridge of nose zone c.) Below the nose tip, above the lip 1. Begin with sizing gauge. 2. Check landmarks. 3. Choose the smallest mask that fits without pinching or obstructing the nostrils. 4. Tighten top straps of headgear, then bottom. Do NOT overtighten straps. 5. Try the mask on with the unit at the prescribed pressure to ensure proper fit. Download Comfort Select Sizing Gauge - Small Download Comfort Select Sizing Gauge - Medium Download Comfort Select Fitting Guide