Scope Control - Variance analysis

Hi,

How can we measure the variance in scope? What mesurements/metrics are typically used in projects?

I can see that the difference between work planned Vs work completed gives an idea of what functionality/components/requiremetns we planned to implement and what we actually implemented.

On a different note, controlling the scope creep is vital here. Is requiremetns stability matrix a metric that we can link to scope variance? The requirements added/dropped/modified when compared to originally approved requirements gives an idea of scope creep. Is my understanding correct? Please share your thoughts.

Thanks,

Chary