The A-depth rating is given for the depth of the topsoil in the soil profile. The rating is expressed in percentage terms. The average topsoil depth for each soil zone receives a rating of 100%. Soils with greater than average topsoil depths for a soil zone are given ratings of more than 100%, while soils with various levels of erosion in the form of exposed subsoil receive a deduction. The previously described master rating is multiplied by the topsoil depth rating.
For example, the A-depth rating of 0.90 on an eroded soil that is moderately eroded (ER10) to strongly eroded (ER25) is an average of 0.95 (ER10) and 0.85 (ER25). This means that the master rating will be reduced by 10% when one multiplies the master rating by 0.90 (100% - 10% = 90%).