Home blood sugar testing kit. This device measures the concentration of glucose in the blood, most often in diabetic patients. A spring-loaded pin (left) is used to prick the skin of a finger to draw a drop of blood. The test probe (white) is placed against the blood droplet which is drawn into a tiny well. This completes a circuit and the device measures the glucose concentration, showing it on a display. Here the concentration is 5.8 millimoles (mmol) glucose per litre of blood, which is within the normal range.