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    Re: Hello
    From: Gary LaPook
    Date: 2011 May 3, 17:06 -0700

    I have attached a photo of the front of the Polhemus showing is set to find the motions for the previous examples.
    Track is set at the top and the ground speed of 240K is in the left window and the latitude of 45° is in the right window. We read out the MOB in the top window next to the Zn. For the 171° Zn (red flag) the correction is minus 1.6' to Hc since the Zn is on a white scale. For the 290° Zn (green flag) the correction is plus 10' since the Zn is on the black scale. We find the relative azimuth on the "Set track inner scale" adjacent to the Zn on the outer scale and if the relative azimuth is on a black scale the sign of the correction is plus to Hc. For the Zn of 171° the relative azimuth is black 81° and for the 290° Zn the relative azimuth is white 20° (covered up by the red flag.) We then look at the "ZN-TR" window and find the MOO correction for the black 81° relative azimuth (yellow flag) is plus 0.6' and for the white 20° relative azimuth (blue flag) is minus 3.8'. The innermost scale gives us the coriolis correction of 4.4 miles (to the right in the northern hemisphere) next to the latitude of 45°. If you want to make a coriolis correction to the Hc instead of moving the AP or the fix simply move the ground speed setting tab to place this 4.4 value adjacent to the "POLE" index on the coriolis scale. Then on the same scale treat the relative azimuth as latitude and take out the individual coriolis correction for each Hc. For the 81° left relative bearing the coriolis correction is plus 4.3' since the body is to the left of the track (northern hemisphere) and the 20° right relative azimuth has a coriolis correction of minus 1.8'.

    These are more precise than the tables in H.O. 249 since you don't have to mentally interpolate.

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