I'm trying to get a pretty detailed understanding of how wages were determined in the USSR under various time periods. My understanding is that at certain times they were piece-rate based, but I'm not able to find how they determined the rate per piece. Was there some sort of objective formulae, is there any primary source documents on this or even a good secondary source that goes into a detailed analysis?
If you can provide any detail for any time period, that would be much appreciated.
I answered your question briefly in r/Socialism but I'll give another response here for people's benefits.
It really depended when you're asking about. Introduced in 1928(The first five year plan under Stalin) was the piecework wages system whereby you're only paid per unit labour that you perform - so for example if you mine X units of coal you'll get paid X$ per unit.
Simply put, there were no consistent wages and people were forced to work harder, longer and in worse conditions than prior to 1928 under Lenin's New Economic Policy. This was implemented to "incentivize" workers into producing above their assigned quotas.
This kind of labour is still common in modern capitalism(Think call centres for example - commission based jobs) but most countries now force a minimum wage on top of that(For example in the US the FSLA was brought in, in 1938, which mandated that piece-rate workers be paid an additional minimum wage). However standard wage rates weren't common in the USSR until the late 50's/early 60's, so from 1928 workers were paid at piecework rates, until the Sixth Five Year Plan under Khrushchev which introduced a minimum wage as part of an overall shift in the direction of the Soviet economy.
How precisely wages were determined at that point(As in, the economics that decided someone would get paid X$/hr) was essentially no different to how the Capitalist economies worked. In Stalin's pamphlet Economic Problems of Socialism in the USSR he asserted that the Capitalist Law of Value was still in place in the Soviet Union - the conclusion to draw from that if you're familiar with Marxist theory is that things like wages and prices and productive output were all decided on the same basis as occurred under Capitalism. So what decided wages that workers got would've been on the basis of the standard or average value produced by the average worker in average conditions - much how wages are determined now, and based on that productive output if a certain amount of profitability was desired then the worker would be paid more or less on that basis.
Sources;
Leon Trotsky: The Revolution Betrayed, IV - The Struggle for Productivity of Labour (1936)
Donald Filtzer: Soviet Workers and de-Stalinization (1992)
Joseph Stalin: Economic Problems of Socialism in the USSR (1951)
A follow-up question, what was the most that one could make via legitimate methods and what job did they have?