http://www.legislation.gov.uk/id/ukpga/1923/20

THIRD SCHEDULE Rules for Determining Percentage of Contributions to Additional Expenses for Damages Payable by a Company.

1

The percentage shall be one hundred if the specified minerals do not extend beyond the boundary of the protected works, and shall diminish by one for every one-and-a-half yards by which the specified minerals extend beyond that boundary on each side thereof.