How is my royalty interest calculated?

Royalty is calculated based on the following:
Take the number of net mineral acres that you own within a well’s drilling or spacing unit (example: If you own an undivided 1/2 mineral interest in 80 acres, you own 40 net mineral acres);
Divide that number by the total acres in that well’s drilling or spacing unit; and
Multiply this number by the royalty interest negotiated in your Oil, Natural Gas and Mineral Lease.
For example, if you own 40 net mineral acres, the spacing unit is 640 acres and the royalty interest is 1/8, then your royalty interest in the well is (40/640) x 1/8 =0.0078125.