Vincent Malmström identifies a correlation between the 260-day cycle and the 260-day gap between zenithal passages of the sun. According to this hypothesis, the 260-day cycle originated in the narrow latitudinal band (14°42′N to 15°N) in which the sun is vertically overhead about 12–13 August and again 260 days later about 30 April – 1 May (Malmström identifies the proto-Classic Izapan culture as one suitable candidate at this latitude). This period may have been used for the planting schedule of maize. However, others object to this conception, noting that while the 260-day calendar runs continuously the interval between autumn-spring and spring-autumn positions alternates between 260 and 105 days, and that the earliest-known calendric inscriptions are from considerably farther north of this zone. Consequently, this theory is not widely supported.