relative standard uncertainty

Symbol u_r. The established standard for the evaluations of the physical constants, reflecting the complications at the quantum level arising from the Heisenberg uncertainty principle, i.e. that measuring one quantity renders others uncertain.

For the values themselves, the standard short form of expression, used in this work, shows in brackets the related standard deviation (σ), applicable at the last digit position of the stated value; the implication is a 68% confidence of the true value being within ±σ of that stated.