This is a well told story of a business breakthrough, a risk taken, and the focus and intelligence of a mid-century Japanese mother of 6 (!) who had to make rice three times a day.
Im guessing Yamada got promoted, but Fumiko did ALL the work on the testing:
Yamada wanted to ensure that the rice cooker worked in all climates, so Fumiko tested various prototypes in extreme conditions: on her rooftop in cold winters and scorching summers and near steamy bathrooms to mimic high humidity. When Fumiko became ill from testing outside, her children pitched in to help.