#13: Day / night indicator, indicates whether it is day or night in the vicinity where you are. You must first set dial “B” though, so that the watch knows which time zone you are in and dial “E” so that it knows whether or not your zone uses daylight savings time. One way to check whether you have correctly set dials “B” and “E” is by going outside and looking at the sky. You may also utilize a window looking toward the outdoors for this same purpose if one is available.