Alexander the great used to take scientists and philosophers with him when he was doing his conquests. This learned men would examine the culture and technology and the resources of the land that he conquer. One of these men discovered this liquid which when exposed to light gradually darkened. Alexander would dip a cloth into this liquid and wear it around his wrist. He used to this to judge what time it was. Among Alexander’s closest advisers this came to be known (say this slowly)
“Alexander’s rag, time band”.