• A change of temperature, pressure (or volume) constitutes an external influence and the equilibrium quantities will change as a result of such a change. (wikipedia.org)
• A balloon is filled with $p_{\text{A},0}$ of molecule $\text{A}$ and $p_{\text{B},0}$ of molecule $\text{B}$. After equilibrium the volume of the balloon is $V_2$ and $p_{\text{AB},2}$ is measured and $K_2$ computed. (blogspot.nl)