A rule for finding the approximate length of diagonal of a square is to multiply the length of a side of the square by $1.414$. Find the length of  the diagonal when the length of a side of the square is $8.3 \mathrm{cm}\text{. }$ 

A rule for finding the approximate length of diagonal of a square is to multiply the length of a side of the square by $1.414$. Find the length of  the diagonal when the length of a side of the square is exactly $7.8 cm$