A base step size value, eps (typically machine precision), is scaled according to the finite difference coefficient order
and function input parameter. The initial scaling according to finite different coefficient order can be thought of as producing a
base step size, h, that is equivalent to RelativeX
scaling. This stepsize is then scaled according to the function
input parameter. Although implementation may vary, an example of second order accurate scaling may be (eps)^(1/3)*(1+abs(x)).