εr                      – Relative Dielectric Constant 

εeff                   – Effective Dielectric Constant

λg                     – Slot line Guide Wavelength

λo                     – Wavelength

A slot or gap with a conducting coating on a dielectric substrate makes up a slot line, a form of transmission line comparable to CPW. The fabrication procedure for slot lines is the same as that for microstrip lines. Along the slot line, the electromagnetic wave encounters the substrate and the air, which serve as its transmission medium. Hence effective dielectric constant is equal to average of both medium’s dielectric constant and the guide wavelength determines the moment of wave in slot line, both of these can be determined using the above calculator.