&gt;  That&#x27;s interesting; shouldn&#x27;t cost-of-input, income, expenditure measures all equal the same amount?<p>In theory, yes, they&#x27;re all the same.<p>In practice, measuring each of the three has its own challenges, which means the raw numbers will differ.<p>It&#x27;s just like physics - you can use the work-energy theorem or Newton&#x27;s laws and arrive at the same result in theory, but depending on the experiment you&#x27;re running, one may be easier to measure accurately than the other, and you&#x27;ll end up with slightly different numbers on paper.