Most interesting. In the early sixyies I made a study of the economics of mechanised working versus handloading and got a peculiar result. If one wanted to maximise return on investment like a good capitalist, then hand loading was better because mechanised pit props were so expensive in a country then short of steel. But if one did a "socialist" calculation using an opportunity cost for capital in addition to depreciation, then mechanisation won easily because labour productivity was so much higher on mechanised coalfaces..

Another important factor developed later. Mechanisation permits longer coalfaces and therefore less underground roadways were needed to move coal. this "concentration" of production lead to very significant efficiency increases. Electricity consumption was a very minor cost for getting coal in the UK. Labour cost(wages, salaries, pensions, and health car were the larget single cost