Sorry, I've never learned "roll" "pitch" and "yaw" in their aeronautical sense...
The Newton has a long axis, which runs through the wind port, and a short axis, which is perpendicular to the long axis.
The short axis should be parallel with the handlebars, though a variation of +/-10 degrees is acceptable.
The long axis should be approximately level with the pavement beneath it. A variation from parallel of +/-20 degrees will work, however.