Tim, the national origin of this tool, we believe, is British. Important to note is the lack of identifying marks, so we can't say for sure. The two features that lead us in this direction is the use of "decimal inch" designations on the 'end of staff matrix' denoting the weight and sizes associated with the GUN, the CALIBER and the SHOT. This ain't French or German, so that pretty much eliminates them as the source. The 9 Pdr. indicates British or French, we believe and it's not French. Colonial forces very rarely had instruments of this complexity or quality unless they were battlefield pick-ups, which perhaps it was. While not an expert opinion, we are never timid about giving information to be considered as educated conjecture. We also think it could have been used on any caliber cannon or mortar, a universal tool.
That's what we think,
Mike and Tracy