The Greeks never drank wine neat — that was for barbarians. They tempered it with water in a great bowl, the krater, and the whole civilised evening turned on the RATIO. Too strong and the symposium descends into chaos; too weak and it is water. Slide the ratio, watch the two pour into one, and tap the blobs to see the whole secret with no numbers at all.
Proportional blending — the exact weighted mean. Wine is taken at ~15% alcohol, water at 0%, so the blend's strength is simply wine-fraction × 15% (computed live as you slide). The historical anchors are real: the Greeks blended commonly 3:1 or 2:1 water-to-wine (~4–5% ABV, a sessionable evening), 1:1 was strong, and akratos — UNMIXED wine — was the mark of a barbarian. Two natures tempered into one by a ratio you can read.
15% for the wine and a linear no-interaction mix are the stand-ins (real ancient wine strength varied and dilution isn't perfectly linear at the palate); the '3:1 = civilised' reading is a historical characterisation. The weighted-mean arithmetic is exact.