where z0* = the estimate at the grid node; λi = the undetermined weight assigned to the primary sample zi and varies between 0 and 100%; zi = the regionalized variable at a given location, with the same units as for the regionalized variable; tj = the secondary regionalized variable that is co-located with the primary regionalized variable zi, with the same units as for the secondary regionalized variable; and βj = the undetermined weight assigned to tj and varies between 0 and 100%.