A person typed some numbers in column A (line 2 to line 10)
then in line 12 she wanted to show the maximum number in the column

to show that value, the only formula I know is .. =MAX(B6:B30)

However, she used the following formula:
=R:R+MAX(B6:B30)

can any one tell me what the "R:R" stands for? and why there is a plus mark?

Thank you