Reference line - how does it actually work?

I have a lot of graphs like this:

image

At first, when I built it ,I thought the reference line would be an hourly average of all data in the dataset but now I realise it’s only the current day.

All 4 lines are built using Table Calculations out of just one measure but basically grouping them into specific time buckets.

Selected day - today 06/09
Previous Days Average - usually the 7 days before current (30/08 - 05/09)
Previous Day - 05/09
Same Day Previous Week - 30/08

When I add a reference line, why is only one table calculation taken into consideration?