Gravimetric calibration in catalysis involves several steps: 1. Selection of Calibration Weights: High-precision weights that are traceable to international standards are chosen. 2. Balancing: The analytical balance is calibrated using these weights to ensure its accuracy. 3. Sample Measurement: The reactants and products are weighed, ensuring that the balance is zeroed before each measurement. 4. Data Recording: The measured values are recorded and compared with expected values to identify any discrepancies.