Tompion Longase

When I opened the door of this clock at my client’s I thought I saw a week going movement. However, when I had it on the bench it appeared to be a month-going clock with 10 pound weights. I tried to obtain confirmation that this was typical of Tompion, but nobody could shed any light on this. So it is up to the reader to reveal some backgorund knowledge about this. I would love to learn about it.