Future scientists and engineers must master fundamental notions of instrumentation. A lab session milestone based on the classical RLC circuit is proposed to check students' theoretical and practical knowledge. Topics include impedance, signal and linear system analysis in the time and frequency domains, as well as the fundamental relations connecting them. The numerical implementation of the Fourier transform and its related pathologies (aliasing and leakage) are also discussed. Practical skills are evaluated through the intensive use of instruments and by presenting and solving potential problems that could alter the accuracy of measurement.