There are three of these 31 day rotation clocks available. Each are standard size drums complete with lid, base and spindle and can easily be fitted to existing barographs - 2 are mechanical (in steel) and one (in brass finish) has a quality quartz movement (this one can be switched from monthly to weekly and even daily rotation). The monthly chart record is neatly condensed from what would be 4 weekly readings totalling 116mm wide (ie, almost 4 feet) down to 29mm recording much more meaningful pressure changes. And of course you only need to change the chart 12 times a year. £325 each