The specifications for manufacturing a steel rod stipulate that the length must be 8.225 ± 0.125 inches.
This means that the minimum length must not be 0.125 inches less than 8.225 inches and the maximum length must not be 0.125 inches greater than 8.225 inches.
A function has a vertical asymptote where it is not defined, and the logarithm is defined only if its argument is strictly positive: it has a vertical asymptote if its argument is zero, and is not defined if its argument is negative.