Hi Andrew, thanks for the answer.

I think I understand now, so it just has some counter (the number of a time series) which is reset to 0 before each run.

Then run called for each bar including LoopBack.

And the series number is incremented each time series called again.

Since the order of calls to series(...) remains the same - it can feed a simple double value to a relevant time series array.

And finally return what it has collected so far for this time series.

That's smart!

Thanks for the clues again!