For each column, you specify the downgrade percentage and whether to reserve minimum trust.
Downgrade Percentage
Percentage by which the trust level of the specified column will be decreased if this validation rule condition is met. The larger the percentage, the greater the downgrade. For example, 0% has no effect on the trust, while 100% downgrades the trust completely (unless the reserve minimum trust is specified, in which case 100% downgrades the trust so that it equals minimum trust).
If trust is downgraded by 100% and you have not enabled minimum reserve trust for the column, then the value of that column will not be populated into the base object.
Reserve Minimum Trust
Specifies what will happen if the downgrade causes the trust level to fall below the column’s minimum trust level. You can retain the minimum trust (so that the trust level will be reduced to the minimum trust but no lower). If this box is cleared (unchecked), then the trust level will be reduced by the specified percentage even if this means going below the minimum trust.