In this work we present a simple mechanical/electrical model for the electrochemical quartz crystal microbalance (EQCM). It consists of a harmonic oscillator (effective mass equal to one half of the crystal mass) coupled to an elastic element and in contact with a viscous fluid. As its electrical analog we consider a RLC series circuit. Simple arguments based on energy/power relationships lead to an easy identification of the mechanical parameters with the electrical ones. That identification together with considerations of the parallel capacitance effects of the electrodes allow us to test/calibrate an EQCM and also to interpret quartz crystal impedance-analyzer results. Model predictions are consistent with the experimental values. This is a subject of considerable relevance for all EQCM experiments.