With this control you can mix options of curves from different channels in the X and Y axis for getting more complex curves in the output. Move the sliders to change the specific weight of the first or second curve in the output signal, or enter values using your keyboard in the appropriate spin boxes fields, or use the spin buttons included in the spin boxes. On the left and right of the sliders there are the preview windows of the first and second surfaces, coming to the input of the mixer. The left sides of the sliders scales correspond to the predominance of the first curve in the output signal, and the right sides - the prevalence of the second curve.
The 'Lock' checkbox located above the sliders gives you the opportunity to make the same weight ratio of the curves mixture in X and Y axes. When the checkbox is enabled the weight ratio of the curves mixture in Y axis will be equal to the weight ratio of curves mixture in X axis. In this case, you can change any of the two ratio parameters and the second will change along with the first automatically.
Also you can lock/unlock weight ratio of curves using the 'Padlock' control. It is located on the right of the spin boxes. By clicking on the 'Padlock' you can enable/disable association between the weight ratios of the curves mixture in X and Y axes. The closed padlock icon corresponds to a bound state of the weight ratios, and the opened padlock icon indicates that the weight ratios are independent.