Because of the symmetry of the parabola, its stationary point will always be in the middle of its x-intercepts (or zeroes). ...
Step 1: evaluate f(x+h) and f(x)
We have


And, of course,

Step 2: evaluate f(x+h)-f(x)

Step 3: evaluate (f(x+h)-f(x))/h

Step 4: evaluate the limit of step 3 as h->0

So, we have

In the metric system, you give a name to the following multiples: 10, 100, 1000, 0.1, 0.01, 0.001, and then you skip three places. So, you have

And thus 0.000001 of something is a micro-something (i.e. one millionth of a certain unit)