What is the first step in performing a substrate correction?

The first step in performing a substrate correction is to calculate the substrate correction value. This value is essential as it adjusts the XRF (X-ray fluorescence) readings to account for the different materials present in the substrate, such as wood, metal, or plaster. Each substrate has its properties that can affect the amount of lead detected, and calculating the substrate correction value allows for a more accurate assessment of lead levels.

Once the substrate correction value has been established, it can then be applied to the XRF readings, ensuring that the results reflect the true concentration of lead in the paint, taking into account the underlying material. This foundational step is crucial in minimizing inaccuracies in lead risk assessments and ensuring compliance with safety regulations.

The other choices represent processes that occur after the substrate correction value has been established rather than as the initial step in the correction process.