Question

Why don't you use the original concentration when testing absorbance and wavelength

Answer 1

never mind

Answer 2

Generally, an average is taken. This is because this "average" is the value that can replace every existing value and give you the same result. This is to avoid error.

For instance, you put in your cuvette with sample and put it in the spec machine, you get 0.032 for trial one, 0.039 for trial two, 1.002 for trial three, and 0.045 for trial four. See how that value might be confusing?