Reading MySQL Slow Query graph on Grafana

I’m having troubles understanding what the graph shows for the MySQL Slow Query graph, particularly with what the y axis represents.
I’ve attached photos of some results I see, I understand the graph shows all slow queries that took longer than the long_query_time variable set. For my case the value is 0.25 . So I’m seeing all queries that took longer than 0.25s. But I thought I would be seeing number i.e. integers in the y axis to show number x slow queries within a specific time frame. But i’m seeing decimals, lower than 0.25 value which confuses me.

I suggest it is slow queries per second. When the x-axis is on the order of second(s), then integral values make sense. When the x-increment is 5 minutes, then I imagine it is sampling every 10 seconds (or summarizing down to that), hence a reading of 0.10 would represent 1 slow query in the last 10 seconds. Be sure to check long_query_time. It defaults to a virtually useless 10 seconds. Crank that down to perhaps 1 (or even some fractional value) to catch more than the egregiously long-running queries.