A thin-walled cylindrical pressure vessel has mean wall thickness of \( t \) and nominal radius of \( r \). The Poisson's ratio of the wall material is \( \frac{1}{3} \). When it was subjected to some internal pressure, its nominal perimeter in the cylindrical portion increased by 0.1% and the corresponding wall thickness became \( \bar{t} \). The corresponding change in the wall thickness of the cylindrical portion, i.e. \( 100 \times \frac{\bar{t} - t}{t} \), is ________________% (round off to 3 decimal places).