Modes
You can switch between simulation modes using the simulation toolbar button:

Simulation Mode
Simulation mode is like a video recording of your trading session. Everything you do goes into simulation files, then you can replay them using the replay mode.
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Replay Mode
Replay mode is like watching a video of what you did in the past. You can use the playback slider to seek any date/time, then you will see everything exactly how it was: your account balance, orders and even all your drawings at the time.