The AZUR apparatus is intended to control the insulating resistance in mine networks with an isolated star centre. The indication of the measured insulating resistance is realised by a pointer meter with a reversed nonlinear scale, which makes it difficult to read. The methodology for the development of an analogue converter is considered here, which linearises the non-linear characteristic current-resistance and, together with a light indicator, the device allows for more accurate and easy reading. An analysis of the error and the measurement range is made.