:'''PosBack''' - a numerical expression, specifying the position:
::'''0''' - open position;
::'''1''' - one position back (the last position closed);
::'''2''' - two positions back, etc.
== Notes ==
* This function can only be used in signals. Please note that if there is a single entry and multiple scalping exits, each exit will have its own entry in this case and the count will increase after each partial exit.