According to Amazon
[here] Its a 15 second slide switch hold for Reset. If you count for 20 seconds (say: "one elephant, two elephants ... twenty elephants") it should reset firs time. Incidentally Off mode is a hold of 4 to 15 seconds, so if you want Off mode, count 8 seconds if you have Voice Guide off. If you have the guide on, it will tell you "Screensaver" for a brief slide or "Turning Off" for a four second hold and you can release it then to turn off. Ignore that and carry on holding for reset.