Why doesn’t the SSC200 compass transmit true heading?

The SSC200 is a magnetic compass, which means that it measures the direction of Earth’s magnetic field relative to the magnetic poles (magnetic heading). This is different than a gyrocompass, which measures heading relative to the Earth’s rotational poles (true heading). This doesn’t mean you can’t get true heading using an SSC200 compass, however, the variation (or the difference in direction to the rotational poles as opposed to the direction to the magnetic poles) must be known. The variation is then added or subtracted from the magnetic heading to arrive at the true heading. You get variation from charts or alternatively from a Maretron GPS antenna/receiver (GPS200). Most displays will accept both the magnetic heading and variation and automatically compute true heading.