It displays when the moon is WAXING (becoming fuller), and WANING (becoming less full).

It displays when the moon is more than half full (GIBBOUS), and when the moon is less than half full (CRESCENT).

So it is easy to PLAN a TRIP ahead and know how BRIGHT the MOON will be then, and what part of the NIGHT it will be in the sky. (However you must allow for clouds, which will reduce the amount of light, depending on their thickness).

Our Moon clocks provide an indication to the phase of the moon during the lunar cycle of 29 days and 12 hours and 44 minutes a rotate.