So I hacked and slashed, and have a switch to get a basic per-game graph.
I need to do a lot of tidying now - just letting you know I haven’t forgotten.
PS: what I like about the per-game rank graph is that there are no step changes in it. This test account didn’t “suddenly” become 8k, as per the by-time graph, that happened over a sequence of 4 games at the beginning, for example.