From Sailing days as I recall the nimonic??? was.
Cadburys Dairy Milk Very Tasty ( compass deviation magnetic Variation True ) or True Virgins Make Dull Company ( true Variation Magnetic Deviation Compass ). A compass on a boat has a deviation card this is split into 360 degrees and gives the error from magnetic that the ships compass displays the boats compass is swung by inserting metal around the compass to try to minimise the error( with all the metal etc on a boat the compass needle is affected this shouldnt happen if you ensure your compass is far from ferrous objects) A good map or chart should have the variation printed on and the amount by which it increases or decreases each year you can calculate the variation for yourself. Having said all that if you can ride a compass bearing closer than three degrees I will be amazed!!!
|