Hi,
I need a small modification to the Smoothed_Momentum.mq4 indicator.
What I want:

Keep the yellow Smoothed Momentum line and all original calculations exactly the same.
Add a dotted central line that automatically sits at the midpoint between the highest and lowest value of the yellow line.
The high and low values are different on every chart, and they also change over time as new extremes appear. The central line must update automatically in both cases.

I tried adding this myself but ran into problems with the chart scale and the yellow line disappearing.

Can you create a clean and reliable version?
Thanks.