B=Fully Functional OEM Screen with small dead pixel, backlight, yellow screen.
C=Fully Functional OEM Screen with Medium shadow with bad dead pixels, stars. Light color marks.
D=Fully functional with OEM Screen 3D Issues, middle color marks in white or black color page. No touch or flex issue, means the screen will flash when you shake the flex cable gently.
For Iphone Oled ScreenA Grade means totally functional OEM Screen, B grade means fully functional with Small shadow or have front glass damaged on four corners, grade C means medium shadows, D means heavy shadows.
Heavy shadows: status bar or icons shadows are very strong in white color, the screen all are pink.
Small dot: Small black dot on the edge, the dots less than 3mm.
Big dots: Big Black dot one the edge, the dots more than 3mm but less than 5mm.