The device itself is small, but the hype around it is big.

Continuous glucose monitors are only about the size of a quarter, but the companies that sell them make huge claims about their health benefits: You can " revolutionize your health ," one company says.

President Trump's nominee for surgeon general, Dr. Casey Means , is a prominent proponent of continuous glucose monitoring. She co-founded a company that distributes the devices and sells an app to help people use them.

The monitor is a painless patch that sticks to your skin. Every few minutes or so, it sends a signal to an app on your phone with an estimate of your blood sugar. (It measures the sugar concentration between your skin cells, which roughly correlates with your blood sugar level.) The app also helps you keep

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