In 1899, Newton's law of universal gravitation was still seen as exact, rather than as a convenient approximation holding for "small" velocities and masses (the approximate nature of Newton's law was shown following the development of general relativity in 1915). Hence Planck normalized to 1 the gravitational constant G in Newton's law. In theories emerging after 1899, G nearly always appears in formulae multiplied by 4 π or a small integer multiple thereof. Hence, a choice to be made when designing a system of natural units is which, if any, instances of 4 π appearing in the equations of physics are to be eliminated via the normalization.