Why might the initial burette reading not be 0.00ml?

In titration, the titre (volume of the solution from the burette) is determined by the difference between the final burette reading and the initial burette reading. Therefore, it is not necessary to make the initial burette reading 0.00 mL.

It is time consuming and difficult to fill the burette and then draw it down to exactly zero.  The easiest thing I've found is to allow the titrant to flow until it is below zero.  Let it stand for 30 seconds and take the initial reading.

This is not a question about Mathematics.  It needs moving to Chemistry.

The Chemistry category is probably a better choice for this question.

As I recall (Chem was a *long* time ago) an initial burette reading is essentially never 0.00 ml.  The primary reason is that there is extra work needed to get that precise level, and almost no reason to go to that effort.  Not needing to subtract didn't count for much, even before calculators were common.