title: String formatting: scale and precision from String.Format
body: <p>I need to format numbers (using WPF converters), and the only way I can do it is via string.Format.</p>
  
  <p>I have two formatting parameters: <em>scale and precision.</em>
  I can achieve what I need separately, but it doesn't work with both:</p>
  
  <p><strong>Example (that works):</strong></p>
  
  <pre><code>string.Format("{0:#,##0,,}", 1234567890.123m) == "1,235"
  string.Format("{0:#,#.000}", 1234567890.123m) == "1,234,567,890.123"
  </code></pre>
  
  <p><strong>What I need:</strong></p>
  
  <pre><code>string.Format("????", 1234567890.123m) == "1,234.568"
  </code></pre>
  
  <p>(which would mean 1,234.568 Millions)
  As you can see I can't find a format pattern that would both scale and also display decimals.</p>
  
  <p>Any idea?</p>