That’s interesting because I have the opposite problem. I started 8 years ago with a clip-on One and had amazing accuracy. I’ve tried Charge 2 (they even sent me a replacement) but both gave me credit for only 80% of my steps. Years later, I tried a Charge 5 (?) and had the same problem. I sent it back. My original One finally died last month so I just got an Inspire 3. Again, I’m not getting credit for 20% of my steps. However, I DO swing my arms most of the time. When I have tried reading from my iPod Touch with my arm extended in front of me, the count is perfect (as it was with the previous wrist band models). So I have a decision to make. Do I want to wear it on my wrist and try to prevent my arm from swinging or wear it clipped to my waistband? (And does it give me all the same readings with the clip as it has with the wrist band. I don’t know yet). Or I can wear it on my wrist and let my arm swing normally, knowing that I’m actually walking 20% more steps than they give me credit for. Having the two options is what made me go for the Inspire.
