The VCR of TSD allows security data to be “played” one bar or tick at a time at varying speeds, in forward or reverse direction.  The main purpose of this is to verify that a System is not cheating by changing entry/exit signals in the past.  As the data is played through the VCR, the price graph is constantly updated, keeping the most current bar visible at the right-hand side of the graph.  This will allow any changed signals (added or dropped) to become obvious, as they will appear or disappear in the “past”.