This totally explains why I’ve had to put an insole in the one that was too big. If you have wide feet or even average feet -you will not be totally comfortable. The elastic in the back keeps these on when shes running around, even though there is about an inch of room in them. If the maximum operating speed is 3/5, and you have a 4 degree range, and have the thermostat set at 78, then at 70 it would be running at speed 1, 74, speed 2, and 78 or greater would be speed 3. For me, with a size 11 foot, I was not quite sure which size slipper to order, since some said the fit was on the large size, and for others a bit small. The quality is good no damages after 8 months use I have issues with my feet. I purchased the Logitech G403 after trying more than my fair share of mice, G602, DeathAdder (Original), DeathAdder 2015, SteelSeries Rival (Original), Mionix Naos, Microsoft Habu, Microsoft Intellimouse. On the plus side it went together fairly easy (I had a helper which made it quicker) and the handles are nice. I bought these for a family wedding.