NOTE 1 The root-mean-square value of a periodic quantity is usually taken over an integration interval the range of which is the period multiplied by a natural number.

NOTE 2 For a sinusoidal quantity $a(t)=\widehat{A}\cos (\omega t+{\vartheta }_0)$, the root-mean-square value is $A_{\text{eff}}=\widehat{A}/\sqrt{2}$.

NOTE 3 The root-mean-square value of a quantity may be denoted by adding one of the subscripts eff or rms to the symbol of the quantity.

NOTE 4 In electrical technology, the root-mean-square values of electric current $i(t)$ and voltage $u(t)$ are usually denoted I and U, respectively.