North Carolina retiree Wayne Nutt has a calculator, and he knows how to use it. During a 45-year career as a chemical engineer, he solved complex problems for DuPont and other companies.

Now he shares his knowledge for free. He writes letters and speaks up when he finds errors in public documents, and he volunteers his expertise when people ask for help. “I like to be able to give it,” said Nutt, who lives in Ogden, just north of Wilmington, North Carolina.