Question: 

What buttons do I need to press to turn the beeper off ? 

Answer: 

Put the clamp to off, then press and keep pressed the Inrush-button and turn the clamp on (turn the dial to VAC). 
When all segments are on press hold for about 2 seconds  and on the screen the text BEEP appears. 
Release hold and inrush button and the beeper is now disabled. 

See this video as well: