Newbie Question: What causes re-painting of an indicator?

[Crassius]

I have noticed that an indicator I am developing gave a sell signal earlier upon application to a new chart with the all the same settings...

It is a volume bar chart. This could be caused by the historical backfill data, as discussed here:

http://www.ninjatrader.com/support/helpGuides/nt7/index.html?how_bars_are_built.htm

beneath" Understanding why a chart may look different after reloading historical data from the server."

I'm not sure if NT went out to the server or not... seems it would first look on my harddisk where I have the incoming data saved, then do a backfill if needed.

I need to naildown if this indicator, which is using EMA's is repainting or if the signal change I noticed is due to reload of data. So, what exactly would cause an indicator like a moving average to change?

What's a good way to nail down for sure that the indicator is repainting?

How does one prevent it from happening?

[NinjaTrader_Bertrand]

Crassius, the EMA is an infinite filter and thus would always take all the data on the chart into it's calcs (albeit very low weighted the farther back you look). When you create a new chart NinjaTrader would always try to reload the current day, thus likely a tick data change caused the issue you saw.

Which CalculateOnBarClose setting were you using?

[Crassius]

Thanks for the reply.

I was using Calculate OnBarClose = True.

I am leaning toward the just a change in the data on reload at this point. I have read many posts that complain about indicator re-painting as people developed them, and I am unclear as to what conditions must be present to cause that.

In this specific case, I am just doing some calcs and taking a double EMA.

I read a section on when NT reloads data from the server, and it would have in this case.

[NinjaTrader_Bertrand]

Yes, then it's very likely a data change causing this - the repaint for example happens easily if you run updates on each tick, where conditions become true intrabar then in realtime thus it appears the signal is present...but when the bar closes price has backed off and negates your signal.