This example shows you how to include fixed covariates in a design.
You want to study the Shrinkage of parts produced by an injection molding process. You have data on 25 batches of raw (thermoplastic) material for potential use in your study. For each batch, you have measurements of Specific Gravity and Tensile Strength, and you have a Supplier identifier. These are your covariates.
You want to study three controllable factors, Temperature (mold temperature), Speed (screw speed), and Time (hold time), on Shrinkage. But you also want to study the effects of the covariates: Specific Gravity, Tensile Strength, and Supplier. Your resources allow for 12 runs. Your resources allow for 12 runs.