 A division ratio of 10, for example, is easy to obtain but not dependable.Chains of bistable flip-flops provide more predictable division, at the cost of more active elements.While not fundamental to circuit operation, diodes connected in series with the base or emitter of the transistors are required to prevent the base-emitter junction being driven into reverse breakdown when the supply voltage is in excess of the "V"eb breakdown voltage, typically around 5-10 volts for general purpose silicon transistors.