KAPLAN question

The sales value of the work done at 31 March 20X9 has been agreed at $22 million and
the estimated cost to complete (excluding plant depreciation) is $10 million. The
specialist plant will have no residual value at the end of the contract and should be
depreciated on a monthly basis Price well recognises progress towards satisfaction of
the performance obligation on the outputs basis as determined by the agreed work to
date compared to the total contract price

Sir what is meant by ” outputs basis as determined by the agreed work to
date compared to the total contract price”?