How do you determine Surface area of leaf without using any instrument?

Here's what you do... take a graph paper.. the 1mm x 1mm graduated. trace the leaf on the graph paper. remove the leaf. then count the whole squares occupied by the leaf. write down the number. count the half 3/4th filled squares and write the number down. count the number of half filled squares and divide the number by two and write it down. leave out 1/4th filled squares. add the numbers you have written down. the number you get is the surface area of one side of leaf. doubling it will give you the surface area of the entire leaf in sq cm