PA Media “Compasses to point true north for first time in 360 years” https://www.theguardian.com/science/2019/aug/30/compasses-to-point-true-north-for-first-time-in-360-years
英国では磁石の示す北が西にずれていたが、磁気偏角は東に移動しており、９月中にグリニッジ天文台（Royal Observatory Greenwich）*1では設置以来360年ぶりに、磁気偏角０、すなわち磁石の針が真北を指すことになる。
とはいっても、日常生活に何か影響が出るということはないらしい。
The line of zero declination, called the agonic, is moving westward at a rate of around 12 miles (20km) a year, experts say.By next month, the compass needle will point directly to true north at Greenwich in London, before slowly turning eastwards.
The Royal Observatory Greenwich was established in 1676 and, from 1839, hosted the specialised magnetic observatory that made continuous measurements from 1840 onwards. In 1926, the instruments were moved to Abinger in Surrey, as electrified railway lines had made it impossible to measure the magnetic field.
Dr Ciaran Beggan*2, a geomagnetism scientist at the British Geological Survey’s Lyell Centre in Edinburgh, said: “At some point in September, the agonic will meet zero longitude at Greenwich. This marks the first time since the observatory’s creation that the geographic and geomagnetic coordinate systems have coincided at this location.
“The agonic will continue to pass across the UK over the next 15 to 20 years. By 2040, all compasses will probably point eastwards of true north.
“It is, at present, impossible to predict how the magnetic field will change over decades to centuries, so the compass may well point east of true north for another 360 years in the UK.”
地理的な北と地磁気的な北との偏差については、
地磁気世界資料センター京都「磁石の北と地磁気極と磁極」http://wdc.kugi.kyoto-u.ac.jp/poles/polesexp-j.html
も。
