I received my Footsie Spa on Friday and promptly set it up. The main dial gives the option of heat, vibration or both. Then there is a dial next to it that is numbered. Nothing in the instructions says what this is. I assumed it was a dial to increase the speed of vibtration or the heat level? However, when I have turned it around, it is really loose and does not appear to do anything? Can anyone tell me what it is for and if it should be so loose? Many thanks.