Well, now that you bring it up I've doubled checked the Big Bearing Compass heading with the navigation map plotter
and I do see a 1 degree discrepancy in what the periscope shows and what the plotter shows SOMETIMES?!? The plotter should be turned approximately 1 degree clockwise on a couple of the nearer ships. However, when I've gone out to the 3000 range areas the compass reading and the plotter bearings are exact!! Like I said, I didn't make the thing, I just scaled it to fit the various resolutions that are used. I'm sorry to have not checked it with a better tool.
Soooooooo, I'm going to fix the images and release the corrected version if I determine this is a big deal or not. If the 1 degree of difference doesn't make a difference to you then go ahead and use what's up on the download. I'll need to make 208 file changes; 13 stock subs x's 16 different mods. I just assumed the darn plotter was corrected for this long time known error of 1 degree off center!!!!! Guess not the version I used. And you know what they say about assuming!!
I'm interested about the error in distance you described though. Where is the error there? If I'm going to rework the plotter and remake the mods I'd like to do it only one more time.