Yeah it's not evaluative, like you're not supposed to calculate it precisely. Here I'll attach some pages of Marx's Inferno that explain my view in a pastebin.

And here's one of the footnotes worth putting up:

I will say that almost all criticisms of Marx on this front presuppose that Marx advances a labor theory of value as an economist, and, since “the central problem of economic inquiry” is “the explanation of the formation of price” (Roll, A History of Economic Thought, 373), the criticisms assume that Marx intends to explain the formation of price by appeal to the labor time necessary for the items bearing prices. It will be easy enough to see from my argument in the main text that I do not think Marx is at all interested in explaining price formation, and that, therefore, the vast majority of criticisms simply miss the target. In this conviction I follow the lines of what is generally called value-form theory. An influential early partisan of the position is Elson, who writes: “It is not [for Marx] a matter of seeking an explanation of why prices are what they are and finding it in labour. But rather of seeking an understanding of why labour takes the forms it does, and what the political consequences are” (“The Value Theory of Labour,” 123). Marx bases himself in a social ontology of cooperation, according to which he can say, for instance, that “social” “denotes the co-operation of several individuals” ( MECW, 5:43; MEGA, I.5:19). Different forms of society, including the global bourgeois society constituted by market interactions, are different forms of cooperation. It is this notion of society as shared labor, that grounds Marx’s conviction that the value of commodities, which mediates their circulation in commercial society, must be the form labor takes in that society.