MT4 open prices testing

[Weiheng Huang]

Hi all, 

I have questions on MT4's 'Open prices' testing mode. I understand that the open of the current bar gives the signal that the previous bar has closed. Trading decisions are then made based on the CLOSE price of the bar that was just completed, or the OPEN price of the bar that just opened?

Should the number of bars in the backtest = number of ticks modeled?

And lastly, I have a reversal system EA (Only market orders) that trades only on bar open. Does this mean that 'every tick' and 'open prices' modes will give the same results? 

I am grateful for your assistance.