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I am attaching a PDF of a plotting sheet I have optimized for the area where I take practice sights.  If you have a vector drawing program (like CorelDraw or Adobe Illustrator) you can create a mercator plotting sheet...and you can choose any latitude you want to define the width of a degree of longitude.  In this case, I chose 53° 15' as the latitude that would define the width of a degree of longitude.

(Plotting the location of my home right on the sheet lets me evaluate, at a glance, the accuracy of my sextant sight.)

I have considered reconstructing this sheet assuming a latitude of 53° 30', to optimize it for the location of my house...which is where I most often take sights from. 

To be honest, though, I have discovered that optimizing your sheet for 53° 00' or 54° 00' doesn't make much of a difference in plotting.  The width of the pencil lead that I use is wide enough that is just doesn't pay to get too anal about the width of a degree of longitude.

I have not experimented to determine the point at which I need to create different mercator sheets for plotting.  My hunch is that if you are near the equator, one plotting sheet is probably useful at plus-or-minus 5° of latitude.  As you move further away from the equator, the need grows for different mercator sheets to ensure accurate plotting. 

Bob

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