The reason for this possible confusion is the following: the law places a hard limit of 750 voters per polling place (article 192.2 of the COFIPE). For districts with a high population density (particularly in cities), usually a single location will contain several polling places in order to split the voters among them (article 192.3.B). These polling places are usually assigned a single number; one is designated as the "basic" polling place, and the others are designated with a second number identifying them as "contiguous 1", "contiguous 2", etc. Each one has its own officials and ballot boxes. However, being in close proximity (often without any physical separation between them) it is not uncommon for voters to be confused as to which box corresponds to which polling place (this kind of error is mentioned several times in Mochán's article; see e.g. pp. 10 and 14 in).