Add scale fix to indicator

I would like to add scale change in my indiactor. Indicator is similar to Directional movement system but with alarmable trend lines.
Right now the indicator fits to scale and there is no room to draw trend line. I would like to add percentage funciton to set scale.
For example:
The maximum of scale is 35, minimum 25. I would like to make scale with 15% reserve. So the scale would start from (1.15x35) 40 and minimum (0,85x25) 21.25 
Note the 15% would be changable in indicator settings.

Payment by skrill or paypal after job.
I deliver indicator to modify.