Backing by the D'Alembert staking plan
Back on a selection according to the D'Alembert plan. The plan itself is described here.
The triggers are very similar to those provided in the trigger example called "Laying according to the D'Alembert staking plan". The only change we made is replace "lay" with "back" and remove the exchange commission correction, as it's irrelevant to this very case.
Here's a screenshot of a sample account statement.