Reference Line moves above visible area in graph

[padmanabhv]

Hello,
I have a simple age histogram. Added a few reference lines, mean, mean+ SD and mean-SD.
This is for all the data.

Now I make selections / filter based on what the user is looking for.
The graph changes (as expected) but the refernce lines go above the graph (and also seem wrong ?!)
Isn't the mean supposed to be of only the values left after selection ? Or am I supposed to make that evident in the formula for the histogram ? Meaning, the formula currently is 
Reference line : Mean=Avg(age)
Is it supposed to be something else, which reflects the age of only selected values ?

And how do I view them ? I can see a small 2 and an up arrow, but cannot click or scroll to see them.

Thank you !

[Channa · Accepted solution]

This case use Combo chart and use second axis

[padmanabhv]

@Channa Thank you !
I ended up using class(age ,10,'Age') for dimension to make it look like bins in a histogram, 
and avg(total age) for the mean reference line and that works just as intended.
Thank you ! 

[padmanabhv]

@Channa 
If you see the graph above, it is missing the [70,80] group. possibly because no data exists.
I would still like to see an empty/blank column there.
Any way to do this ?
Thank you