The article considers a way to expand the capabilities of the dynamic method for measuring hygroscopic points (equilibrium water vapour pressure over saturated solutions of substances) of solubles by applying it to an ordered series of substances with their hygroscopic points in a narrow range of (68–76)% RH. The experimentally measured values of hygroscopic points are proposed as reference data on the hygroscopicity of such substances as carbamide, rubidium chloride, sodium nitrate, strontium chloride; the values for barium bromide and lithium perchlorate are clarified. The capability of the dynamic method to measure the difference between the hygroscopic points of substances enhances its consistency and reliability, makes it possible to present reference data in a structured form. Along with the simplicity of the procedure and the laboratory equipment used, this makes the proposed version of the dynamic method highly competitive among the other methods for determining water vapour pressure over saturated solutions of substances.