Why does my iPhone usage not add up?

Settings > General >Usage
It says "2.9 GB available" 9.9 GB used. I have a 16 GB iPhone. 9.9 and 2.9 don't add up. Where's the remaining 3.2 GB?Why does my iPhone usage not add up

The remaining 3.2GB is what was on the phone when you bought it. (FaceTime, calendar, Siri, etc.) You did not get exactly 16GB.

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