Working environment - Altitude
In order to comply with some safety regulations and standards, especially related to creepage and clearance, the insulation characteristic of the air is considered. At high altitudes, the air's insulating characteristic changes, and so does the the electronics' behaviour. In the case of oscillocopes, it is probably even more sensitive due to its high speed electronics / bandwidth and the possibility of reducing the isolation between some traces or components (source of noise due to coupling).

More to that in here