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However, production not only involves labor, but also certain means of labor: tools, materials, power plants and so on.
These means of labor — also known as means of production — are often the product of another labor process as well.
So the labor process inevitably involves these means of production that already enter the process with a certain amount of value.
Labor also requires other means of production that are not produced with labor and therefore bear no value: such as sunlight, air, uncultivated land, un-extracted minerals, etc.
While useful, even crucial to the production process, these bring no value to that process.
In terms of means of production resulting from another labor process, LTV treats the magnitude of value of these produced means of production as constant throughout the labor process.
Due to the constancy of their value, these means of production are referred to, in this light, as constant capital.

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