One of the most practical and little used barograph clock types is the one with the monthly rotation.
It creates a condensed chart record of a full month’s reading on to a single 300mm wide chart.
The same record on four weekly charts joined together would spread over about 1200mm - that’s over four feet in old money!
You can see on the picture below that atmospheric pressure highs and lows will feature much more dramatically as they are condensed and are, of course, no less accurate.
For the casual observer, changing a barograph chart and winding the clock drum 12 times a year is a lot less of an effort than having to do the same chore 52 times over the same period. Of course, you need to ensure the pen nib and ink are suitable as they track less than10mm per day, so you need to be sure the nib is not too thick and the ink has to be the right viscosity, otherwise the ink will simply ‘feather’ over the chart.
I always recommend the classic French ‘bird beak’ nib type as it draws a nice clean and crisp line. Alternatively, you could fit a fibre nib which works very well - not for purists though!
Feel free to contact me if you need more information.
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