I have the questions.

1. You described about
#property indicator_buffer 1
Why do we need this buffer? What is it?

2. We wrote:
double ExtMapBuffer1[]
And you described about arrays. As I understand we may use
int my_array [2] = {30, 70}
when
#property indicator_minimum 0
#property indicator_maximum 100 and we need to draw two horizontal lines (for example).
And if not 30 and 70. But 30.5 and 60.5 we will use double instead of int?

3. Why
double ExtMapBuffer1[] ?
Is it always ExtMapBuffer and we need just remember it?

4. int ExtCountedBars = 0
It means we are counting everything using curent zero bar. But in some cases we need to xalculate high or low for 300 bars for example.
Should we use
int ExtCountedBars = 300 ?
But if we need to change it from time to time we will use in property?
#property ????