A calculator can combine the numbers you provide consistently, yet it cannot infer the official rules behind a gradebook. Two courses may display the same weighted percentage and assign different outcomes because their thresholds, precision, missing-work policy, extra credit, or category rules differ. Treat the arithmetic result as a transparent check, then compare it with the syllabus and official grade record.
Identify rules outside the formula
Letter-grade thresholds can vary, and some systems use no letters at all. One instructor may round 89.95 to 90 while another keeps more precision. A gradebook may drop the lowest quiz, cap a category, treat missing work specially, or apply extra credit after the ordinary weighted sum. None of these choices can be recovered safely from scores and weights alone.
Use a three-part verification
First confirm every entered score and weight against the official gradebook. Second verify whether the current grade is normalized over completed work or already includes missing work as zero. Third read the syllabus for category weights, dropped items, rounding, curves, and extra credit. If the official result differs, the documented course policy is authoritative; GradeCalc remains a percentage arithmetic aid.