In what units are the wavelength scales on a Smith chart calibrated?

The outer perimeter of a Smith chart contains scales used to determine the impedance transformation that occurs when adding lengths of transmission line to a circuit. These scales are calibrated in fractions of a transmission line's electrical wavelength. They are typically marked as 'Wavelengths Toward Generator' (WTG) rotating clockwise, and 'Wavelengths Toward Load' (WTL) rotating counter-clockwise. Using electrical wavelength as a standardized unit allows the Smith chart to be universally applied to any transmission line, automatically accounting for the velocity factor.