In realms where natural constants, l0, t0, or v0, of length, time, and/or velocity, are present, dimensionless secondary quantities can be defined of the form Q′ = f( l0/l, t0/t, v0/v, etc.) are not, in general, expressible as a constant×the product of powers of primary quantities. It is suggested that dimensionless quantities of the form Q′ are required in the theory of interactions.

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