The governing authority shall thereupon determine the number of mills and fractions thereof, which will be required to provide for the payment of all statutory and ordinary charges and all other obligations, contractual or otherwise of the subdivisions, omitting therefrom any debt secured by special taxes, and none other.
This computation shall be based upon the assessed valuation of the taxable property of the political subdivision and it shall be ascertained by reference to the last assessment for parish or municipal purposes previous to issuing the bonds.