Hi,
When we move from a percentage (out of 100) based performance measure to finding defects out of 1 million, then we use sigma calculations. Six Sigma level processes have only 3.4 defects in 1 million opportunities. The DPMO (Defects per million opportunities) calculation shown in the Excel sheet reflects the same. Alternatively, you can visit isixsigma.com to calculate the DPMO based on defects found in your processes and determine the performance level in sigma terms. It is akin to measuring in milliseconds to differentiate performance levels; if we measure in seconds, everything may appear equal.
Please let me know if you need further clarification or assistance.