The meaning of the lunar phase terms in bronze inscriptions is a difficult problem in W. Zhou chronology. The present article presents a method which avoids the questions of historical date and reign length of each king, and instead investigates the possible range of meaning of each lunar phase term by means of the relational constraints imposed by the calendar dates themselves. Seven groups of materials were selected, each having two or more lunar phases and calendar dates so their separation in days could be calculated. Within each group of inscriptions arithmetic constraints then make it possible to establish the range of days to which the lunar phase term could possibly refer. The results obtained from the seven groups are all consistent： jishengpo and jisipo ought to refer to the waxing and waning halves of the month, respectively. Churl refers to certain days at the begin- ning of the month, probably the first occurrence of the auspicious heavenly stems （gan）.