Unmatched sets of Nessler Color Comparison Tubes- The top graduation line on unmatched Nessler Color Comparison Tubes may be any distance from the bottom, but within the scale lengths shown in the table below. Matched sets of Nessler Comparison Tubes- The graduation lines of all the nessler color comparison tubes in a matched set will not vary by more than 3 mm from that of any other tube in the set. The distance of these lines from the bottom of the tube may be anywhere within the scale lengths shown in the table below.Tubes feature a "Shadowless Bottom" and durable white ceramic enamel rings and legend. Rings coincide with specific volumes of liquid.