Underproof

If it didn't ignite, the solution had too much water in it and the proof was considered low or "underproof". ❋ Unknown (2010)

- Jesus,  it's not underproof, he says, screwing the water out of his eyes. ❋ Unknown (2010)

But in some ways he was a kind of Thackeray several degrees underproof -- a small-beer ❋ George Saintsbury (1889)

Multiply the result by the quantity of spirit, and divide the product by the number obtained by _adding_ the _required_ per centage overproof, or _subtracting_ the _required_ per centage underproof, to or from 100, as the case may be. ❋ George William Septimus Piesse (1851)

Thus, spirit of wine at 56 per cent. overproof, signifies that 100 gallons of it are equal to 156 gallons of proof spirit; while a spirit at 20 per cent. underproof, signifies that 100 gallons are equal to 80 gallons at proof. ❋ George William Septimus Piesse (1851)

Summer Edition is a bit underproof compared to regular Beefeater (80 proof, or 40% ABV, instead of 94 proof), but the delicate summer botanicals add a sweetness you might not often find. ❋ Unknown (2010)

_overproof_ per centage _to_ 100, or _subtract_ the _underproof_ per centage _from_ 100. ❋ George William Septimus Piesse (1851)