NavList:

Dan, which plotting board did you get?  Pictures of your plots are always nice.

I am afraid I cannot help you with trying to adjust IC on a Kollsman.  The abbreviated technical manual I found for it does not include this.  I've never had one where the IC was so bad that I thought I really wanted to zero it out.  I just figure out the IC for both rising and falling objects and use that.  Note that I find with the Kollsmans that the IC for rising objects is close to but not always the same as the IC for falling objects - given that this is all gear driven inside the sextant, I am not entirely surprised at this.  The good news with a Kollsman is that I find the IC consistent over time and conditions.

If you should figure it out how to adjust IC, please do let everyone here know.

In case you are wondering at what point do I start to get unhappy with a bubble sextant's IC, I have two Tamaya bubble sextants (Coutinho pattern which Bill also has a writeup on in his sextantbook blog) that I have used for Sun and star fixes and each of those are off by more than 60' (in opposite directions!).  I just take the IC that the sextants give me and apply to the Hs.  A much more conservative approach than trying to break loose the 85 year old screws to adjust the bubble.