How does the Georgia Tech recalculate your High school GPA?

How does the Georgia Tech recalculate your High school GPA?

From the admissions website:
“If your high school does not provide a GPA or you have attended multiple high schools, we will recalculate a weighted 4.0 GPA (0.5 points added for AP, IB, Dual Enrollment & AICE courses) using core courses only.”

https://admission.gatech.edu/first-year/academic-preparation