The value of labour power is, like all other commodities, determined by the labour time necessary to produce this special commodity. What is needed are those commodities that sustain the life of the labourer and enable them to reproduce their labour-power every day, and to reproduce the next generation of workers, their children. Of course there are some other commodities which have been won by the proletariat, and in certain societies, and even within the working-class itself, these will vary. Thus, the working-class get more than just subsistence wages, at least, in most societies that comprise the First World this is now the case. To put it slightly differently, it is the difference between the value of the commodities at the beginning of the production process and the values at the end of the process.
Machinery can increase two forms, or forms of extraction, of surplus-value.
Machinery can both increase absolute and relative surplus-value. The longer the worker works so the more surplus-value they produce and so the more profit they make. If the capitalist gets them to work an extra hour then the surplus-value produced is one hour greater. The introduction of machinery allowed for, and indeed created under the conditions of capitalism, the situation in which the length of the working day actually began to increase. In order to get as much time as possible many capitalists stooped to the most disgusting methods.