" content="Current-meter (cm) instruments determine directions from onboard compasses,
so interpreting velocity components in geographical coordinates requires that
magnetic declination be taken into account.  This is what the present
function does (see &amp;#8220;Details&amp;#8221;)."><meta property="og:description" content="Current-meter (cm) instruments determine directions from onboard compasses,
so interpreting velocity components in geographical coordinates requires that
magnetic declination be taken 