[John Gronberg]

Installed a Gentex mirror with compass. The instruction call for a Zone calibration of "9". Other instructions call for "8". I live just outside Chicago and these two zone maps differ
in the number to adjust to probably because Chicago is right in between, help.

 

[basscatt]

Installed a Gentex mirror with compass. The instruction call for a Zone calibration of "9". Other instructions call for "8". I live just outside Chicago and these two zone maps differ
in the number to adjust to probably because Chicago is right in between, help.

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it isn't that critical - just pick one or the other -

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looking ar Ranger's map -
obviously - go with zone 8 -

 

[Submariner409]

The differences between "zones" of magnetic variation (declination) is just a shade over 1 degree - and driving E - W will change "zones" pretty quickly in your area. Don't sweat it.

Look at this isogonic U.S. map .......... The numerals along the bottom of the map are the variation figures. Looks like Chicago lies on the 1 West figure for 1980. Over here, on the upper Chesapeake Bay, the current variation is 11 W.

 

[Ranger]

GENEVA IL
Latitude: 41° 53' 15" N
Longitude: 88° 18' 19" W
Magnetic declination: -3° 14'
Declination is NEGATIVE (WEST)
Inclination: 69° 20'
Magnetic field strength: 54028.4 nT

In believe this is the zone map in your owners manual.
We are in ZONE 8