The angle of the bar changes as the person pushes it down...how can you ensure it's at a 90 degree angle? These old fashioned stadiometers are pretty inaccurate sometimes because of that.
It depends. but yeah some people measure taller when facing the wall (including me) than they do leaning against it. Possibly because your lumbar spine is slightly curving inwards whenever you put your back against the wall. But this isn't always the case, since some friends i've measured have measured taller when they lean against the wall vs. facing the wall. So in conclusion, there is nothing wrong in trying both methods.
