This recording mechanism uses a rectangular chart. It could be supplied in sizes to cover as many as 60 stations and for time periods as long as 72 hours. The mechanism pictured here is for 20 stations and a recording time of 48 hours. The drum rotates once in 12 hours, but after each rotation it is shifted axially a small amount so that it presents a new column of paper  to the recording pin of each station on the next 12 hours, and then a new column for each of the ensuing 12 hour periods.