DavidAI

I am a type 1 diabetic and have been since 1966 almost 50 years. The technology has changed so much since I started with having to boil my glass and stainless steel syringes and sharpen reusable needles. Blood sugar testing was only available at hospital visits every 3 months. I now use Abbots Freestyle Libre 2 which penetrates the skin and stays attached to my arm for 2 weeks at a time before I change it. I have to scan the device with my iPhone to get a reading (for me that's about 15 times per day),
It is more convenient than finger pricking but nothing like as accurate. It is off either + or - 20 points on each reading when compared with a finger prick device. This is deemed normal by 'the diabetic specialist who prescribes it. 

I wonder how much the proto-type Apple Watch sensor is off? if it's more than this the FDA is correct in not approving it.  

I would suspect the companies that make the 2 most common current devices approved, the Freestyle sensors and the Dexcom G6 CGM have the FDA in their pockets, and the standard they impose for Apple is higher than this simply because it's 'Apple'.