weird rotation of axis X,why?

ok,here comes a strange one:

i created a cube(without changing the rotation or scale…) and attached a simple script:

function Update()
{
  transform.eulerAngles.x+=1;
}

and the cube stopped when the x rotation reached to
90???

why? everything seems ok,what’s wrong with the math stuff?

The documentation tells you explicitly not to do what you are doing.