Furuno FMD-3100 Operator's Manual page 212

12. NAVIGATION TOOLS
How to select range calculation method
The range calculation method for the range rings can be selected to Rhumbline or
Great Circle. Do as follows to select a calculation method.
1. Open the menu, then select [NAV Tools] and [Geometry] to show the [Geometry]
page.
2. Select [Rhumbline] or [Great Circle] with the drop down list box for [Rings].
3. Click the [Save] button to save the setting, then click the close button to finish.
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