Where base units come from and how they are related to each other? The second, the metre and other base units are useful approximations for describing our universe. What we measure are mere ratios among measured values and base units. The fundamental question is how... It is difficult to accurately describe real circumstances in nature or technology. We can certainly determine general equations, see thermodynamics, with an accuracy of tens of percent. The rest can be fine-tuned ‘by trial and error’ based on estimates, experience,... All beauty in the world is not free, but needs boundary conditions – external or internal limitations. See solids, liquids and gases. For all beauty, formative art, craft, science, is expressed in solids, liquids, or gases. The more beautiful, the more gentle.... All mechanics is based on solids (or sufficiently bound matter). Mechanics deals only with materials (atoms, molecules) in the solid state. Where there are no solids no rigid bodies, there is no mechanics. You might argue what about hydromechanics or aeromechanics... It would be better to write in the order of randomness, probability and necessity. For at the beginning is randomness of pure chaotic behaviour then the probability of the states or events and at the end necessity od states, forms or events. Such is already a feature... 
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