There are disclosed novel uses of aziridine compounds. The invention provides a system and method by which a program administrator for a company may model varying client-imposed limit scenarios in order to determine one or more optimal monthly andor transactional spending limits. The slots are arranged along the trailing edge between the root and the tip of the blade substantially perpendicular to a longitudinal axis of the blade, at least the slot closest to the root of the blade presenting an inclination towards the tip of the blade lying in the range 10 to 30 relative to an axis of rotation of the blade. Each of the amplifier circuits includes a first transistor having a first input node that receives an input signal transitioning across a range of high and low voltage levels, and a second transistor having a second input node that receives a reference signal. The take up spool is incorporated into the handle of a toothbrush. The housing and the duct section are coupled by a coupling member.