The opening range changes as new highs and lows are seen. You wont get a flat horizontal line because the new highs and lows change in this period.
I had suggested to use Brushes.Transparent to make the plots invisible so the chart scaling does not adjust the scale to show the plot line at 0.
If you want the same visual result, but wish to use the indicator in the Strategy Builder, just set the plot brushes to Transparent and leave the Draw.Line code in place.
Further changes than this would require more intricate modifications to the script.
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