RE: An oddd request
RH is relative humidity. I picked up a cheap digital weather thermometer a few months ago ...... gives pretty good temp and rh info on the display.... I think it cost all of $5.
The "Fat" part of the pipe is the end of the divergent section. You can usually see where the weld line is between the front and rear pieces.
Dub did set it up, but that measurement was not likely recorded. It is important to know the pipe length since it is related the rpm and engine power.