The perils of rounding; or, Careful with that Axe, Eugene

In the image you'll see two displays for a single weight measurement I conducted recently on a Qardio Base scale. Qardio sells a number of devices that can measure various things and report those measurements to your phone. I have a Qardio Base for my weight, and a Qardio Arm for blood pressure. The first Qardio Base I had was flaky, and fortunately Qardio replaced it. Yay, Qardio! The new one seems to work pretty well -- except that is does weird things with my measurements, which is the purpose of this post. I use these devices with my IPhone. These products will save the measurements to Apple Health. But I also manually copy the measurements over into a spreadsheet so I can see a lot of different data in one place and analyze them.

Check the image. This is the very same measurement, only the second display is taking place a minute later. Note the BMI values. When I stood on the scale and took the measurement, the BMI is reported as 24.9. rounding.png

However, a minute later, the measurement is 25.0.

This is especially annoying because 24.9 is in the "normal" range, while 25.0 is in the "overweight" range. So I notice that. I've been trying to lose weight recently, and this discrepenacy drives me pretty crazy. Which is it, Qardio? Get your story straight!

Thus, I have noticed that the BMI calculation will sometimes change within a few minutes of the original measurement. The discrepancy can be triggered by completely shutting down the app and restarting it -- and then looking at...

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