Experience. Many have said this. Now some might not notice the difference 2 or 3 %, a few days will make. Others have noticed 10-15% difference. The settings sort of settle in. Like a sponge, it will take on water, but it will take a few minutes to fully soften up when it is totally dried up. I got on the higher 10-15% myself, when mine sped up. Each might be different.