Mix and Yield Variance

Hi John, Could you please help me understand what is the difference between - Mix Variance and - Yield Variance Taking Materials as an example. Would I be correct in saying - Mix looks at the cost of materials. If a (F) variance, this means we have used more of the cheaper material in the mix. Yield looks at the quantities (input) of raw materials used in production (output). If a (F) variance, this means we have used less raw materials in the product than we expected for the level of output produced. Thanks Maurice