where pd is the product of pressure and distance, and A {\displaystyle A} and B {\displaystyle B} are the gas constants for calculating Townsend's first ionization coefficient and γ {\displaystyle \gamma } is the secondary emission coefficient of the material. As the pressure increases, the distance between the electrodes must decrease to achieve the same breakdown voltage. This law is proven to be valid at inter-electrode distances as small as tens of micrometers and pressures higher than atmospheric.