The StartBlockUndoRedo method starts recording the UI operations as a block on undo/redo operations (equivalent of EndBlockUndoRedo method of the Chart object). The method has effect only if the AllowUndoRedo property is True. The EndBlockUndoRedo method collects all undo/redo operations since StartBlockUndoRedo method was called and add them to the undo/redo queue as a block. This way the next call on a Undo operation, the entire block is restored, so all UI operations are restored. For instance, if you have a procedure that moves several bars, and want all of them being grouped, you can use StartBlockUndoRedo to start recording the operations as a block, and call the EndBlockUndoRedo when procedure ends, so next call of an undo operation the bars are restored to their original position. The EndBlockUndoRedo method must be called the same number of times as the StartBlockUndoRedo method was called. For instance, if you have called the StartBlockUndoRedo twice the EndBlockUndoRedo method must be called twice too, and the collected operations are added to the chart's queue of undo/redo operations at the end.