The degree of disturbance of the sample collected by the sampler is expressed by a term called the “area ratio”. If the outer diameter and inner diameter of the sampler are $D_o$ and $D_i$ respectively, the area ratio is given by

- $\dfrac{D_o^2-D_i^2}{D_i^2} \\$
- $\dfrac{D_i^2-D_o^2}{D_i^2} \\$
- $\dfrac{D_o^2-D_i^2}{D_o^2} \\$
- $\dfrac{D_i^2-D_0^2}{D_o^2}$