Hi,
For your information, Clock DIN is tighter than MIDI or USB on DrumBrute (IN or OUT). This is because with clock DIN, the machine has just to deal with a clock edge interrupting (almost) everything the machine was doing before, whereas in MIDI or USB, it has to sort and dispatch serial messages (polling method about every 300µs). However, even in MIDI DIN or USB, the DB is still very tight. If your tempo displayed moves a lot, with a great amplitude, it is due to your apparatus that is master.
Try syncing two DrumBrutes together in MIDI DIN or Clock DIN, and you will see the tempo displayed is not moving. It only moves after the dot because of rounding computing concerns.
Y.