Single point line options?

I’m trying to work out a solution to displaying a “high water mark” for one of my graphs. Effectively, I have a graph representing response times to a service, and I’d like to have an additional horizontal line representing the max value that response time has reached.

I can add the single point without issue, but since I’d need to do it with max(value), I only have a single point being returned.

I can create a DB entry for each time the response times are checked I suppose, and just check if the max has changed, and create a one-off entry for each run, but that seems like I’d be adding unnecessary data.

I did look at including the max as part of the graph series label, but that unfortunately is restricted by the current time view. I need to somehow display this value regardless of the time shown.

I did find I could at least add it as a second query, and then have the value in the tooltip, but if the time it happened is outside the displayed time period, I then get the “data outside of time range” message across my graph, which I can’t avoid either.

I understand “why” I don’t get a line from a single data point, but I’m hoping there’s maybe an option for “extrapolating” or something? Anything I might have missed?