Chart gain/loss

is not my code actually its a example in
Pine Script™ and charts become better acquainted
becaus is can useful and it unpublished i just publish that without any channges

As a trader scrolls or zooms on their chart – causing the range of visible bars on the chart to change – scripts using either of these new built-ins will automatically re-execute so that calculations and visuals can adapt to the new context. This opens the door to a whole new variety of scripts that dynamically adjust to changes in the range of visible bars.

This indicator draws an arrow from the open of the first visible bar to the close of the last, and shows the gain/loss for that range