# CalibrationReport CV-RMSE and NMBE computation

In the UtilityBill measure, the formulas for computing NMBE and CV-RMSE include an 'n-1' rather than just an 'n' in the denominator. For example:

Source: https://github.com/NREL/OpenStudio/bl...

```
result = 100.0 * std::pow(squaredError / (n - 1), 0.5) / ybar;
result = 100.0 * (sumError / (n - 1)) / ybar;
```

Why doesn't the formula just use 'n' as described in the definition, e.g. https://www.kw-engineering.com/how-to...

Thank you