................(1.14)
A vector can be represented as sum of its orthogonal components,
...................(1.15)
In general u, v and w may not represent length. We multiply u, v and w by conversion factors h1,h2 and h3 respectively to convert differential changes du, dv and dw to corresponding changes in length dl1, dl2, and dl3. Therefore
...............(1.16)
In the same manner, differential volume dv can be written as 
and differential area ds1 normal to 
is given by, 
. In the same manner, differential areas normal to unit vectors 
and 
can be defined.