The instrument must have come in contact with a permanent magnet which has altered the polarity position of the floating magnetic needle in the instrument thus throwing it off course. However if the reading is consistent you may continue to use it by compensating it by 90 deg
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The instrument must have come in contact with a permanent magnet which has altered the polarity position of the floating magnetic needle in the instrument thus throwing it off course. However if the reading is consistent you may continue to use it by compensating it by 90 deg