Tick charts, last print 1% or more above or below the market where do they come from?

[wilburbear]

Chart then returns to normal. This happens in most stocks. Just saw it in SPY.

Which exchanges allow a "print through"?

 

[cgeorgan]

From my experience these are average price prints, or prior negotiated block trades.

 

[mikesmithv]

If IB is your broker try selecting any exchange but "SMART" for charting. SMART can occasionally grab stale data and cause just what you describe. You want to specify a real exchange when you subscribe for real-time data.