So how are tick charts drawn?

I want to start trading with Sierra chart but i want to make sure that data is right, and it just doesn't look right. On TradeStation I have drawn a trend line matching the lows of the circled areas. Notice how the price pokes below the trend line in the rectangle? This is a 2000 tick chart with 5 days data with session times 15:30-15:15 Eastern time.
05.30.2012-08.02.18 - keymoo's library

This is an open ecry chart of the same thing. Notice how price breaks the trendline exactly as TradeStation does, although the chart is slightly different.
05.30.2012-08.06.36 - keymoo's library

This is NinjaTrader from another trader, notice how it is identical to TradeStation but very different to Sierra. Why does Ninja match TradeStation precisely, but no matter what settings I change Sierra doesn't want to match any of them?
05.30.2012-08.37.03 - keymoo's library

This is Sierra Chart with infinity demo data feed. Notice how on this chart price barely breaks the trend line. This kind of data difference can affect how I trade and I need the data to be spot on. Why are there differences?
05.30.2012-08.12.38 - keymoo's library

Sorry for the large images, I have a big monitor.

Answer: data feeds are not equal, and almost certainly nothing to do with the platform (except for TradeStation, which forces you to use TradeStation data).

Read:

Analysis and comparison on different data Feeds and Platforms for Bid/Ask Studies Hi All, I wil try here to do an analysis and comparation on different data feeds and platforms to perfom studies involving bid/ask data, like comulative bid/ask difference or delta bars and footprint like. Luke. P.s. Is not a simple work, and take …

Mike