Think with congruent triangles. If I have 40 thou of error out at a distance of 8" (rough size of bell), then out at 20" (lenght of block), it's about 100 thou.
What you write makes sense but i don't understand why the on line calculators keep giving the wrong answer??? When I punch in .040" rise over 20" the calculator says .114" which is what you are saying.
