Confused about ramzi theory🙈

Dont mean to sound thick as two short planks lol! But can someone explain the ramzi theory? I know left indicates boy right indicates girl but on which sort of scan? Do you flip it if the scans done vaginally or abdominal? For example if had abdominal scan & baby was on the right of the scan would it not be flipped & be girl or be flipped & be a boy? I know it's all fun I just wondered 😊😊