Abstract: A measuring instrument for the thermal and/or reactive properties of one or several samples of a solid, liquid or gaseous substance, comprising a measuring cell constituted by an electronic component suitable to detect a temperature difference between two regions on it's surface. The instrument includes a thermal inertia block defining an inner chamber in which is contained the measuring cell and which block is provided with an opening above the measuring cell and a skirt surrounding the chamber. The skirt extends vertically downwardly to an essentially horizontal bearing surface.