"HealthKit removes some of the error from patients' manually entering their data."
"patients, who will be sent home with an iPod touch and instructed to enter blood sugar levels in between doctor visits."
So instead of manually entering the data on paper, they are manually entering into an iPod Touch - and subject to a tiny keyboard and Autocorrect - instead of getting the data, it'll enter, "I'm on my way!"

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The

Watch does not have a blood sugar lancet, er, um, sensor, so it would be of no use.
I recall the rumors talking about the Watch measuring blood sugar, blood pressure, oxygen saturation - but it does none of that - only heart rate.
So, health kit only replaces apps that allowed people to enter data manually or connect the phone to all kinds of medical equipment. It consolidates those other apps, most of which were buggy. But anyway, the watch only does HRM, and we have to hope it's accurate - I'm not looking forward to Heart Gate.