Without the input from a course gyro, the SN90 system will not be able to present correct navigational information. In most cases a suitable course gyro is already installed on the vessel.
NoteMost global positioning system (GPS) can provide course information, but this data is generally too inconsistent to provide
a stable presentation on the SN90 system. This inconsistency is especially noticeable at low vessel speeds. Incorrect course information can then result in settings not working properly.
We recommend that you use a satellite compass or a gyro compass.