Abstract: An electrochemical-sensing apparatus for analyzing a sample of a user. The apparatus has a housing with a port for receiving an electrochemical-sensor structure having a counter electrode (CE), a reference electrode (RE), and at least one working electrode (WE) for contacting the sample, and an analysis circuitry for coupling to the electrodes for analyzing biomarkers in the sample, and an output for outputting an analytical result. The analysis circuitry has a circuit for generating an excitation signal and applying it to CE and RE, at least one frequency analyzer for receiving a return signal from the at least one WE for analyzing the sample, and a set of switches for short-circuiting CE and RE and for engaging at least one calibration resistor to CE/RE and the at least one frequency analyzer for directing a calibration signal to the at least one frequency analyzer component for calibration.