Answer
precision $\frac{1}{9}\ in^2$
GPE $\frac{1}{18}\ in^2$
Work Step by Step
The smallest unit is $\frac{1}{9}\ in^2$, so that is the precision.
Greatest possible error is half the precision.
$GPE=\frac{1}{2}\times\frac{1}{9}=\frac{1}{18}$