(1) An importation that you make is partly creditable if it is a * creditable importation that you make only partly for a * creditable purpose.
(3) The amount of the input tax credit on an importation that you make that is * partly creditable is as follows:
"extent of creditable purpose" is the extent to which the importation is for a * creditable purpose, expressed as a percentage of the total purpose of the importation.
"full input tax credit" is what would have been the amount of the input tax credit for the importation if it had been made solely for a creditable purpose.
(4) The Commissioner may determine, in writing, one or more ways in which to work out, for the purpose of subsection (3), the extent to which an importation is for a * creditable purpose.