Editing Smith chart (section)

===Actual and normalised impedance and admittance===
A transmission line with a characteristic impedance of <math>Z_0\,</math> may be universally considered to have a [[characteristic admittance]] of <math>Y_0\,</math> where
:<math>Y_0 = \frac{1}{Z_0}\,</math>
Any impedance, <math>Z_\text{T}\,</math> expressed in ohms, may be normalised by dividing it by the characteristic impedance, so the normalised impedance using the lower case ''z''<sub>T</sub> is given by 
:<math>z_\text{T} = \frac{Z_\text{T}}{Z_0}\,</math>
Similarly, for normalised admittance
:<math>y_\text{T} = \frac{Y_\text{T}}{Y_0}\,</math>
The [[International system of units|SI unit]] of [[Electrical impedance|impedance]] is the [[ohm]] with the symbol of the upper case [[Greek alphabet|Greek letter]] [[omega]] (Ω) and the [[SI unit]] for [[admittance]] is the [[Siemens (unit)|siemens]] with the symbol of an upper case letter S. Normalised impedance and normalised admittance are [[dimensionless]]. Actual impedances and admittances must be normalised before using them on a Smith chart. Once the result is obtained it may be de-normalised to obtain the actual result.