The bottom line of the display shows the raw data in the input buffer with the most recent data to the right and old data to the left.
You can turn the knob to move your view point into the MIDI input buffer.
The top line of the display shows the offset into the buffer on the right and your adjusted position in the middle.
"MIDI of- 6 7800"
"< 55 F7 00 00 00"
This shows that there are extra 00s after the end of a SysEx message. The offset is 6 so there may be 6 additional 00s that you would see if you turned the knob.
This is not a tool you would use often but can be a life saver if you are getting unexpected behavior from your code.
Background image by Pauline Moss. at http://paulinemoss.deviantart.com/art/Stars-307119758