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Ron,

As an alternative to plotting and avoiding scale issues, I recommend looking into Motion of Observer (MOO) approaches to calculating a fix. MOO is simple to use and handles running fixes nicely when two or more sights are being advanced or retarded to a common time (observer have changed position between sights).

Gary LaPook has posted extensively about this, a common technique for air navigation. MOO tables are in the inside covers of HO249 vols 1, 2 and 3 as well as a yellow supplement card.  He has also posted tables with speed ranges more suitable for yachtsman. The formula is trivial and works super for any speed or times. The resulting correction to Ho can advance or retard a LOP to a common time for a running fix.

A tecnical paper by George H. Kaplan, "The Motion of the Observer in Celestial Navigation", U.S. Naval Observatory , Washington, D.C., Undated. shows various approaches, one of which is the MOO formula. Andres Riuz's amazing navigational algorithms programs also deal with this.

While Excel is a lovely interface, it is not so practical at sea, my opinion only.