17-2 Setup > Chart
Press 
twice, then select Chart:
Rotation
The options for chart rotation are:
North up: North is always at the top of the chart window.
Track up: The chart is rotated so that the boat direction is to the top of the display. This option is useful for navigating narrow harbours or rivers. The 657 asks for a course deviation resolution; this is how much the boat direction needs to change to make the chart redraw.
Tip: If the chart redraws too frequently, increase the course deviation setting.
Course up: This option is only available if the boat is navigating to a destination. The chart is rotated so that the plotted course to the destination is vertical.
Palette
Select the color scheme for the LCD display. The options are:
Normal
Sunlight: Brighter colors, more visible in sunlight.
Night: Reversed colors for night, to preserve night vision.
Map datum
657 GPS positions are based on a worldwide reference (datum) known as WGS 84. Most paper charts are based on WGS 84. However, some paper charts are based on other datums In these cases, the latitude and longitude coordinates of objects on the 657 chart window are different to the latitude and longitude coordinates of these objects on the paper chart. This applies to all objects, such as the boat, waypoints, tracks, lines of latitude and longitude and cartographic features such as land, rocks, buoys and depth contours.
Use Map datum to select the 657 map datum to match the datum of the paper chart. Then, the latitude and longitude coordinates of objects displayed on the 657 will change to match the corresponding coordinates on the paper chart.
Setting map datum
1In the Chart setup menu, select Map datum.
2Select the map datum for the paper chart you are using.
3If you select a datum other than WGS 84 the 657 asks if you want to apply the NMEA datum offset (see below).
! WARNING
When you change to a chart with a different datum, change the 657 map datum again.
62 | Northstar Explorer 657 Installation and Operation Manual |