A method of evaluating effective sampling steps of auto focus is provided. The modulator changes the apparent orientation of one retarder stack relative to the other so that, in a first switching state of the modulator the two retarder stacks cooperate in filtering the spectrum of input light, and in a second switching state the two retarder stacks complement each other, yielding a neutral transmission spectrum. The rectangular wire is wound, by multiple turns, on the core member, and the multiple winding structures are disposed, in a stacked state, along the axial direction of the core member. The electrical connector may be a male universal serial bus electrical connector, a Type-A USB electrical connector or a mini-USB electrical connector having electrical connections for electrical power, ground, data and ID. A method of correlating bacterial biofilm formation within an operational microbial fuel cell directly to current output.