Assumed position (AP)

The assumed position is the reference latitude and longitude a navigator adopts to compute the altitude and azimuth a body should have, so a sight can be reduced by table. When using sight-reduction tables (HO 229 or HO 249) the assumed latitude is the whole degree nearest the dead-reckoning latitude, and the assumed longitude is chosen so that the local hour angle comes out a whole number of degrees, since LHA equals GHA minus west longitude (or plus east). From that AP the tables give Hc and Zn. The intercept Ho minus Hc is plotted from the AP along the azimuth.