It's not necessarily more accurate to use 69.3. If you expand the Taylor series to two terms you get an even better formula, 69.3/x+0.34. Write it as (69.3+0.34

It's not necessarily more accurate to use 69.3. If you expand the Taylor series to two terms you get an even better formula, 69.3/x+0.34. Write it as (69.3+0.34x)/x and it shows how, as the interest rate grows, using a dividend in the 70–72 range is more precise than 69.3. [That's another way to write the paragraph "A note on accuracy" from the article]