A behaviour and properties of an accuracy of differential positions of points in continuously operated geodetic networks were investigated. For this purpose mathematical modeling and real GNSS-data processing methods were used. As investigation results these properties were revealed. Appropriate features of measurement data processing were explained for the better accuracy characteristics of differential positions of points, and a «proper reference frame» as a suitable tool for its usage was defined. Possibilities of its usage in various geodetic jobs were shown, such as: control point’s extention, localization and local geoid modeling, differential point position’s accuracy cataloging and control points coordinates’ full variancecovariance matrix reconstruction.