With high atmospheric pressure giving us a prolonged period of hot weather, it’s a good time to calibrate our barometer, something that I’ve never got around to doing since I inherited it from Barbara’s dad.
According to the Met Office website, the pressure today should remain stable at 1020 millibars, which is equal to about 30 inches of mercury, classed as ‘Fair’ on the barometer. Our reading was just 10 mbars out, so it needed no more than a quarter turn of the small screw on the back to put it right, which is pretty good after twenty or thirty years.
It’s an aneroid barometer so the adjustment changes the tension of a spring which is there to prevent the pressure-sensitive metal chambers inside it collapsing.
It would have been impossible to calibrate the thermometer on the day that I drew this sketchbook page in early spring, 2014, when a low pressure system was sweeping across Britain.