Error <= PI(n+1) - PI(n) < (1/10)^n

##</code><code>##

  Error <= [ PI(n+1) - PI(n) ]^2 < ((1/10)^n)^2

##</code><code>##

   PI = sum( i = 0 .. INF ) (-1 ^ i) / (2 * i + 1)