The Failure Direction for a Slide model is specified on the General page of the Project Settings dialog. You may choose either:
Right to Left
Left to Right
In general, modeling options in Slide are NOT affected by the choice of Failure Direction (i.e. it is NOT necessary for the user to account for the Failure Direction while creating a model).
NOTE: the Defaults button in the Project Settings dialog allows you to save the currently selected Failure Direction as the default direction for all new files.