NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2015 Jun 7, 11:50 -0700
Yes, you've got it right. conceptually, if the watch is slow the actual time of the observation is later, the GHA and LHA should be larger than you used for your computation so the LOP and the fix is actually further to the west. Making the corrections in your table accomplishes this, moving the fix and LOP to the west equal to the change in GHA.
But, in normal marine practice, you make the correction for the watch error at the beginning of the computation, determine the correct GHA and place the AP at the correct longitude to produce an accurate LOP and fix.
O.K., here's a sceanario. You take your observations and plot your LOPs. Then, sometime later, you get a radio time signal and discover that you watch has an error. Instead of going back and computing all the LOPs again from the start your just apply the corrction from the MOB table. But, why not just move the fix west of east based on the longitude changing exactly the same as the change in GHA?
In flight navigation the MOB table is used as part of the preplanning for a fix and it simplifies and speeds up the computations, which is very important in a plane moving at 7.5 NM every minute. See my description of this on my website at:
gl
