A band of leather attaches a flat circular stone to your wrist, with a white top half and a black bottom half. Pressing on the center of the stone causes a small triangular piece of metal to pop up and cast a shadow (regardless of lighting conditions) showing the time of day, and pressing down on the triangle causes it to fold over and lock back in place. The transitions between black and white mark sunrise and sunset, and the shadow is accurate to within one hour. If you travel to another plane of existence it will automatically adjust itself to the new day/night cycle or equivalent, though there is no indication of what the equivalent measurement would be. If there is no equivalent, the triangular piece will not lift up.