SB wrote:
I'm going to stick my neck out and ask a very newbie type question.
Rodney mentioned reading "True" rather than "Magnetic." I've puzzled
for a while now over why we would use "True" at all. I know... I
should know...but I don't.
The compass is obviously "Magnetic" and it would be used for taking
bearings while under way. That data is then transferred to a paper
chart that has a compass rose with a magnetic measurement in it.
In short, when would one use the "True" measurement on a chart, when
reporting ones position to another, in a electronic charting program
or any other occasion?

Blushing Bob

Since the position of magnetic north is changing perpetually, it is standard
practice to give all bearings etc, in true notation, and apply the
correction factor appropriate to the time and location of the navigator.

The compass rose on charts, where magnetic north has moved almost as soon as
the chart is published and sold, is for guidance only.

GPS bearings and calculated courses are corrected for magnetic north as at
the time and place of the fix shown on the screen, but the user has the
option to display in true notation if he/she so pleases. I personally set my
GPS to true readout, but others may prefer to set theirs to magnetic.


Remove "nospam" from return address.