A rear view mirror for a vehicle has certain asymmetrical aerodynamic features that are combined with construction details that render the assembly invertible for use on either side of the vehicle and easier to install than its prior art counterparts. A voltage difference V between two spaced apart electrodes is brought to a selected value and held, the holdoff time interval \u0394t required before gas discharge occurs is measured, and the associated electrical current or cumulative electrical charge is measured. Accordingly, it is possible to transmitreceive service data having a format different from that of the existing method in a single MH system.