The formula that uses relative cell references is F18+F19/2.
A relative cell reference will adjust as a formula is copied because it is actually working by calculating what the formula is in relation to the cell where the formula is. For example, if you copied this formula down one row it would adjust to F19+F20/2. This is opposite of an absolute cell reference like you see in the first example. The cell will always reference cell A10, regardless of where it is copied to.
