First off, thank you for this great tool and the available resources the team provides. I have thoroughly enjoyed learning the ins and outs. I was reading through the Dash Tutorial, particularly the subsection entitled, Update Graphs on Hover at the following link: https://dash.plotly.com/interactive-graphing
I think it is possible that the final two @app.callback functions are mistakenly misnamed. Specifically, def update_y_timeseries and def update_x_timeseries.
In the case of def update_y_timeseries, it is taking inputs from the x-axis of the parent graph, and making a time series.
In the case of def update_x_timeseries, it is taking inputs from the y-axis of the parent graph, and making a time series.
There are no syntactical errors, but I believe this could be confusing for others reading the tutorial for the first time.