In project management, variance is the difference between a planned cost and the actual cost incurred and, normally, this leads to corrective actions. A more general definition of Variance Analysis can be found in Wikipedia and other sites.
Variance Analysis
At Time Now:
Ei
= Initial Estimate (Planned or Estimated Budget)
A = Actuals = Actual amount incurred
Et-c
= Estimate-to-Complete
Ea-c
=
Estimate-at-Completion = A + Et-c
Va-c
= Variance-at-Completion = Ei - Ea-c
At New Time (Time Now + T):
If the variance is high (too much error or discrepancy), then assign Ea-c as the new Ei.
Hence,
Ei
(new time) = Ea-c (time now)