French term (edited): �cart

Judging from the bit in brackets, this is a reference to what my economics textbook (Lipsey) calls marginal or incremental analysis. This, in economic theory, measures the impact of producing one more of a thing in terms of marginal cost - the cost of producing the extra 'thing' versus the marginal revenue - the income you get from selling the extra 'thing'.
In practical accounting terms, here, they are looking to see whether taking on a new order is financial viable: they look at the marginal costs of the order - the extra raw materials, extra staff costs [overtime?], power, transport - well, you get the idea - required to fulfil it, and compare that to the marginal income, i.e. the income earned purely from that order alone.

(NB:écart in accounting can also mean variance, but that usually means the difference between budget and actuals, and doesn't appear to be meant here)

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Note added at 2 hrs 3 mins (2005-02-11 12:10:47 GMT)
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After your note: you could be more literal - a calculation of the marginal requirements should be possible at any time to simulate the impact of a particular order on requirements for components, etc.

I thought the key point was your understanding of \"écart\"? And I just trying to explain that when they say \"par écart\", they mean \"marginal\", in the English economics/accounting sense. Use it however you like with the words around it :-) If you want to be more literal, and in your second example, I see no reason not to be, then be a bit more literal :-)