A single pill can be crushed, dissolved in water, and when a drop of the solution is placed on the paper, it turns yellow if the drug is present.The intensity of the colour indicates the level of the drug, which can be compared to a simple colour chart.The researchers at OSU took the system a step further, and created an app for an iPhone that could be used to measure the colour, and tell with an even higher degree of accuracy both the presence and level of the drug.