The device looks like a long thermometer with two ends. One the left end the user would place a solution containing antibody A and on the right end she would place a solution with antibody B. Then a drop of blood would be placed in the center, followed by a drop of the dye. The solution would travel down the paper and reach both antibody solutions. If the blood type was A, then the left solution—with a combination of antibody A, antigen A, and dye—would turn brown, and the right solution—with a combination of antibody B, antigen A, and dye—would turn teal. If the blood type were B, the left solution would be teal and the right solution would be brown. Type AB, in which both antigens are found on red blood cells, would turn both solutions teal, and type O, with no antigens at all, would turn both solutions brown.