Yes, different universities use different scales (4.5, 4.3, or 4.0) and may have different grade breakpoints. Always check your university's academic regulations and select the matching scale.
Most universities replace the original grade with the retaken grade. However, some schools cap the maximum grade for retaken courses (e.g., B+ maximum). Check your university's retake policy.
Use the calculator twice — once entering only major courses, and once entering only general education courses. This gives you separate GPA figures for each category.