Which mass-produced consumer product is often credited with helping to unify the American nation after the Civil War by standardizing time across the country?

Throughout history, certain consumer products have had profound impacts on society and the course of historical events. Some products have even influenced major historical turning points or revolutions in how people lived their daily lives. This trivia question challenges your knowledge of a particular product that played a significant role in American history during a crucial period of national development.

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Singer sewing machine
Waltham pocket watch
Colt revolver
Kodak Brownie camera