Damn THR switch does different things at different times! Never understood it. Just learnt by heart when to press it during stressful times! As far as I could see, it 'bumped' the power setting to the next setting, sometimes. When one of the cabin crew once brought a visitor up, a young boy, they primed him to point up and say 'what does that button with T-H-R on it do?' He was nearly strangled.