The real-time barograph published on this page is derived from a Meteor2000WX precision barograph with a calibration traceable to an NPL standard. Between 980 and 1020 mB it is accurate to +/-0.4mB and outside this range to +/- 0.6mB. The sensors are recalibrated yearly against an NPL absolute standard and exhibit a long-term drift of not more than 0.27mB/year. The readings are corrected to sea level using the standard UK equation due to Laplace, which you will find with a helpful calculator here. In addition to the barometric trace, a time-derivative plot is also provided and these data are also used to obtain a 4 hour forecast using the Negretti-Zambra algorithm described here. The trace is uploaded every 5 minutes.