This paper examines ways to increase the effectiveness of the Distance measuring units (DMU) algorithm. DMU algorithm can be shown as a three independent algorithmic blocks: algorithm of digital filter (DF) for current and voltage input signals; algorithm of the impedance vector measurement; the algorithm of the tripping characteristics for protection operation. The efficiency of the individual blocks operation is estimated by their corresponding criteria with the using the appropriate measures. In this paper the most attention was focused on the ways to improve the efficiency of the impedance calculation algorithm of the earth fault distance protection.