# Weighted Average

*subtopic to measurement*
[under construction]

### Bi-Directional Average

An average ratio of two numbers, similar within a factor of 2x, exists either arithmetically or geometrically as, (a/b)-(b/a) / 2 or sqrt( (a/b)+(b/a)-2 ). [I've used this when comparing planets twinning: for example Venus:Earth is .82:1.0 for 1.22-.82/2 = 20%]
[under construction]

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