I'm not trying to 'debunk', just trying to understand. When economic planners in a communist state are evaluating goods, I understand the logic of totting up the total amount of labour embedded in each microwave or onesie, and using that as a unit of value-measurement.

But goods unquestionably do involve materials as well as labour, and why leave out one really obvious factor of production?

Yes, I know that acquiring metal from the earth requires labour-hours, and so the metal can be said to be a fruit of labour. But if it's a resource that can be depleted (like metal, like a non-renewing aquifer) then it has to be economised. And if it has to be economised, surely it has to be reckoned in the accounts of the planners?

Say I invent a way to make a car-part with the same amount of labour but 10% less steel, how would that be evaluated under the labour theory of value?

Thanks