Barograph and Other Weather Recording Instruments FAQ's
Why is my barograph drawing a straight line?
If the pen is drawing a straight line across the chart it could be that the pen arm is pushing too hard on the chart. This often occurs in pre-1940 instruments which have a knurled nut at the linkage end to tighten or slacken the arm towards or away from the clock drum.
The nib should just touch the paper - ideally, it’s only the ink on the end of the nib that needs to reach the chart.
To check you’ve made the correct adjustment, gently push the pen arm up the chart about 20mm and let it settle back, then repeat the process down 20mm and let it settle back. The pen should return to the same place on the chart.
Most post-war barographs are fitted with a reverse ‘C’ profile or gate suspension developed in the 1930s. Because the arrangement is also slightly angled it therefore relies on gravity to allow the pen arm onto the chart without pressure and therefore eliminates the friction at that point associated with earlier models.
Check also the alignment of the links between the top of the bellows which can deviate over time. Looking from the right-hand end of the barograph towards the bellows make sure they are all in line and upright as the slightest disparity can cause friction.
Do bear in mind during calm anticyclonic weather there can be very little movement in the pressure reading over several days.
2. How can I tell if my barograph is working?
If the pen arm is pointing down at the bottom of the chart, although rare, it could be the bellows have blown which would be extremely difficult to repair.
Check the linkages from the top of the bellows through to the pen arm, these sometimes become tight.
Unless you are fortunate to have a pressure chamber a simple test is to find a large clear polythene bag, seal any holes for leaks, then carefully place the barograph (without the lid) inside the bag, close off the opening and gently inflate the bag. Make sure the pen arm is clearly visible then push gently down on the inflated bag. You should see the pen arm rise then the fall back to its original position when you release the pressure on the bag. Even if the pen arm moves only slightly it probably means the bellows are still actually functioning and the mechanism simply needs a good service.
Generally, barograph clocks are of a good quality manufacture and spare parts can normally be obtained, even the mainspring and escapement. I have found that a good service and clean by a competent horologist will usually keep the clock running for many years.