You need to be as precise as your resolution, otherwise the precision is meaningless. I guess you could argue that your resolution is units of half-billion (since some things are measured like that), but the initial value of 0.1B, and your use of 0.5 rather than 'half' suggests a resolution of 0.1B.
This is different to the aphorism 'The difference between a million and a billion is about a billion', both because of the difference in scale, and the quoted resolution.
You need to be as precise as your resolution, otherwise the precision is meaningless. I guess you could argue that your resolution is units of half-billion (since some things are measured like that), but the initial value of 0.1B, and your use of 0.5 rather than 'half' suggests a resolution of 0.1B.
This is different to the aphorism 'The difference between a million and a billion is about a billion', both because of the difference in scale, and the quoted resolution.