A flip-flop includes an input stage to receive a data signal and an output stage to provide an output signal. The device 10 includes a first portion 12 that is secured, via a shank portion 16, to a tool providing rotary force, and a second portion 14 that transfers the rotary force to a preselected fastener via a plurality of arm members 30. The two terminal sets are set on the circuit board corresponding to the two encoders respectively, and each terminal set is composed of two terminals which is not connected to each other. Each node includes a hinge which is joined via a transition region to a strut. By using the method of the present invention, measurement of the density of fluid to be detected by a calibrated piezoresistive micro-cantilever may be achieved within seconds or even shorter. The process involves reacting RfCH2CHFRf with a basic aqueous solution to produce a product mixture comprising RfCH\u2550CHRf.