The characteristic in $\log \left(0.025\right)=-1.602$ is 

Since the value of algorithm is negative, we cannot directly write $-1$ as the characteristic and $-1.602$ as the mantissa.

We will try to convert the decimal part into a positive quantity. Adding and subtracting 2 to $-1.602$, we get

$\log \left(0.025\right)=-1.602+2-2=(2-1.602)-2=-2+0.398$

Now we have the decimal part as positive, so the characteristic becomes $-2$ and mantissa is 0.398. it is also written as $\overline{2}+0.398$ (read as2 bar $+0.398$)