Please, correct my poor english

These icons are shortcuts for Chart → Field of Vision. Here you can set the width/hight of the displayed field of vision of your active chart to a predefined value (in degrees of arc). A click on the last icon sets the FOV to 360°.

You can change the default settings for the fields of Vision by Setup → Chart, coordinates → Field of Vision.

Each icon set corresponding cardinal point as point of view for the chart. Same as Chart > View Horizon.
Last icon set local Zenith as point of view.

If you are interested in objects situated in one of the cardinal directions, simply click the appropriate icon to make your choice:

• N for North,
• S for South,
• W for West,
• E for East,
• Z for Zenith

Setting the chart by these methods to one of the cardinal directions, also forces the chart to use the Altitude-Azimuth coordinate system.