What is the test for a variation in the terms of s. 17 of the Divorce Act?

In the case of Dolson v. Dolson [2004] O.J. No. 4197 Heeney J. stated at paragraph 70 as follows: To the extent that any differential treatment is to be accorded s. 17 applications as compared with s. 15(2) applications it appears to be confined to the remedy to be granted by the court. Assuming that the judge has found a variation to be justified he or she must start from the proposition that the initial order was fit and just and fashion an order that takes account of the changed circumstances in a way that still gives due weight to the original order which reflects the parties understanding of what constitutes an equitable sharing of the economic consequences of the marriage.