Add Japanese Hydrometer Scale support with conversions and localization

[Nishiwaki-Takao]

Summary

This PR adds JapaneseHydrometerScale, a dimensionless quantity for Japanese hydrometer readings derived from reciprocal specific gravity.

The quantity includes:

• Reciprocal specific gravity
• Heavy Baumé
• Light Baumé
• Sake Meter Value

It also provides conversions from the scale to Ratio as specific gravity and to an equivalent Density using the density of water at 4 °C as the reference.

Definition

Let specific gravity be $SG$, and define reciprocal specific gravity as:

$$ R = \frac{1}{SG} $$

ReciprocalSpecificGravity is used as the base unit of JapaneseHydrometerScale.

Heavy Baumé

$$ ^\circ\mathrm{Bé}_{\mathrm{heavy}} = 144.3(1-R) $$

Equivalently:

$$ R = 1-\frac{^\circ\mathrm{Bé}_{\mathrm{heavy}}}{144.3} $$

Examples:

• $SG = 1.000$, or $R = 1.000$, gives $0,^\circ\mathrm{Bé}_{\mathrm{heavy}}$
• $SG = 1.200$, or $R \approx 0.8333333$, gives approximately $24.05,^\circ\mathrm{Bé}_{\mathrm{heavy}}$

Light Baumé

$$ ^\circ\mathrm{Bé}_{\mathrm{light}} = 144.3R-134.3 $$

Equivalently:

$$ R = \frac{^\circ\mathrm{Bé}_{\mathrm{light}}+134.3}{144.3} $$

At $R = 1$, the light Baumé value is $10,^\circ\mathrm{Bé}_{\mathrm{light}}$.

Sake Meter Value

$$ \mathrm{SMV} = 1443(R-1) $$

Equivalently:

$$ R = 1+\frac{\mathrm{SMV}}{1443} $$

At $R = 1$, the Sake Meter Value is zero.

Motivation

These scales are conventional hydrometer readings used in Japanese industrial and brewing contexts. They are not plain ratios: each scale has its own name, formula, abbreviation, parsing behavior, and localization requirements.

Representing them as a dedicated quantity provides typed conversions between the related scales while keeping their convention separate from a generic Ratio.

Design

The new quantity is named JapaneseHydrometerScale, with the following units:

• ReciprocalSpecificGravity
• DegreeBaumeHeavy
• DegreeBaumeLight
• SakeMeterValue

Reciprocal specific gravity is used as the base unit because all three scale conversions are affine functions of it.

The implementation also provides:

• ToSpecificGravity(), returning a Ratio
• ToDensity(), returning an equivalent Density

ToDensity() uses a water density of 999.974950 kg/m³ at 4 °C:

$$
\rho_{\mathrm{sample}}

\frac{\rho_{\mathrm{water},,4,^\circ\mathrm{C}}}{R}
$$

The resulting density therefore depends on that explicit reference condition. Reciprocal specific gravity is not treated as density itself.

Implementation

• Add the JapaneseHydrometerScale quantity definition.
• Use ReciprocalSpecificGravity as its base unit.
• Add heavy Baumé, light Baumé, and Sake Meter Value conversions.
• Add English and Japanese abbreviations:
  • 1/SG
  • °Bé heavy / °Bh
  • °Bé light / °Bl
  • SMV / 日本酒度
• Add ToSpecificGravity() and ToDensity() conversion methods.
• Generate the quantity type, unit enum, parsing and formatting support, number extensions, localization resources, and generated tests.

Tests

The generated tests cover:

• Conversion of one reciprocal-specific-gravity base unit to every supported scale
• Conversion through As() and ToUnit()
• Round trips between the base unit and each scale
• Parsing and formatting of English and Japanese abbreviations
• Number extension methods
• Standard quantity operations and metadata

The custom conversion expectations verify that $R = 1$ gives:

• Heavy Baumé: 0
• Light Baumé: 10
• Sake Meter Value: 0

Scope

This PR implements the Japanese hydrometer convention represented by the formulas above.

It does not attempt to provide a generic or internationally interchangeable DegreeBaume unit. Other Baumé conventions, API gravity, and Twaddell scales may use different constants or reference conditions and remain outside the scope of this change.

References

[- JIS Z 8804 : 2012 液体の密度及び比重の測定方法] (https://kikakurui.com/z8/Z8804-2012-01.html)
- Authoritative reference for the Sake Meter Value formula.