How to display the time tracker in a chart with a custom variable as X array

I am plotting some data in chart over time. If I use the Time as the X array name, the time marker can be shown in the chart. However, If I change the X array name to another variable, in my example, avg(alpha) I can’t see the Time tracker anymore:


Could you please help me?

If you change the X array to be something other that Time, it no longer makes sense to show a Time marker since there’s no assurance that the Time marker will even be straight vertical line. For example Time 0 and Time 1 may have the value for the avg(alpha) and in which case both those values will be plotted as the same X location.

Thank you for your reply.
I wonder if there is any workaround to that, something like: displaying a dot that moves on the chart according to time value.