Joseph used the spreadsheet below to check the sensitivity of Innovative Speakers profit to increases in prices of components by suppliers next year. First he raised the cost of cabinets by $20\%$ in cell B$12,$ then noted the profit change in B$6.$ Next he raised the cost of diaphragms in C$12$ by $20\%,$ then noted the profit change. He repeated these steps for electronics and assembly. What mistake is Joseph making?