... Principle of Operation: At the beginning, green led light on the upper half, then flows ... sand. ... Principle of Operation:At the beginning, green led light on the upper half, then flows to the ... seconds, the screen will turn to yellow, the sandy clock will show “3, 2, 1”, then screen turn ... 2. Display order of the color is adjustable.3. The operation is completed by key-press. LED sandy clock traffic ...