In order to recognize revenue,it must be possible to measure the amount of revenue that has been earned with a reasonable degree of assurance.

This is a fundamental principle of revenue recognition as per Generally Accepted Accounting Principles (GAAP). Revenue can only be recognized when it can be measured reliably. This means that the amount of revenue earned and the associated costs can be determined with a reasonable degree of certainty, and there is no significant uncertainty as to the collectability of the revenue.