There is a mod for SH3, where the fellow took the 500 yard display of the Line Tool on the NavMap, and has it able to display 100 yard increments, dependent upon the zoom level. I'm not certain that has been converted to SH4 or not, but realistically, there is minimal need for such precision. You could try using an external search engine, such as duckduckgo, and use "site:subsim.com/radioroom measurement" or maybe " NavMap" or both, or whatever, and that might find what you're looking for in that regard. converting it to SH4 would be a matter of using a different location in the menu_1024_768.ini file (and yes, I did dip the hissop in the bucket and smeared it on the door posts, as well as throwing a pinch of salt over the left shoulder after invoking that file name)...
- or just wait for someone else to come by that remembers the mod.