Declination, or compass direction, (D) is the lower trace on each image and the horizontal force (H) is the upper trace. Universal Time is the time recorded here (astronomical) plus 12 hours and measured D precedes H by approximately 12 hours.
For reference the marked 'solar flare effect’, beginning at 23:15 recorded time on August 31st, is at 11:15 Universal Time on September 1st. It has been measured as 110 nT in H and 0.283 degrees in D.
Please note that these timings are approximate and should not be regarded as definitive. Also note, the size and scale of each image is only approximately similar, day-to-day. Some data have also been lost, either due to ink and paper degradation, or because the variations were so large they were off-scale.
This is one example of the historical data contained in the British Geological Survey geomagnetic archives. We have digistised our complete collection of over 250,000 magnetograms which are now available to view online.