<p><pre><code>   15 by default is reasonable for everyday programming; 
   we don&#x27;t need results like 0.30000....4 popping up in
   our faces.
</code></pre>
That just changes the problem. You can&#x27;t get rid of rounding error by representing decimal numbers in binary. 0.3 - 0.2 - 0.1 still won&#x27;t show up as zero even if you only display 15 decimal digits.