Confusion between pitch/roll and huge drift

[X-Y]

Hi, there are a couple problems I'm wondering about:

1. The tutorial doesn't seem to mention which axis is pitch and which is roll. From the values, rotation along the long axis seem to be pitch, the short axis seem to be roll. Is that the case(I would imagine the other way around)? Would be nice to make a illustration to clarify.
2. The pitch value is getting a very huge drift after I rotates the board around for a short while. If I rotates it for a round, it sits at +-1.0