In what decade was the binaural stethoscope (with two earpieces) first invented, replacing the original monaural design and establishing the foundation for the modern stethoscope design we recognize today?

The stethoscope is one of medicine's most iconic tools, but its design has evolved dramatically since its invention. This poll tests your knowledge about a significant product design innovation that revolutionized how healthcare professionals use this essential diagnostic instrument. See if you can identify when this critical design transition occurred, transforming medical practice worldwide.

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1850s
1820s
1890s
1920s