In recent years, the no-insulation (NI) winding technique for rare-earth barium copper oxide (REBCO) pancake coils have been attracted in the field of high magnetic field generation. A contact resistance between turns characterize the stability of REBCO pancake coils. Hence, it is important to control the contact resistance, as well as it is necessary to measure it. The sudden-discharging method is a popular way to measure the turn-to-turn contact resistance. It is, however, not robust against various conditions, e.g. external field, varying temperature, etc. A few years ago, we have been proposed a method to measure a contact resistance of an NI REBCO pancake coil applying a low-frequency-ac current, so called an LFAC method. We present the validity of LFAC method through a simulation. Since the original LFAC method contains some errors, we will show a correction method together with simulation results.