I'm reading a paper, when this article refers to the function:
$$\beta(v)=\frac{(\frac{v}{I})^k}{1+(\frac{v}{I})^k}$$
It say that "around the $I$, $\beta$ is approximately linear in $I$, and has a slope of ca. $\bar{\beta}=\frac{k}{4I^k}$ ".
What is the meaning of this phrase? What is the meaning of ca?
Thanks.