# Change Log

## Version 2.1

This fixes 4 defects of the specification itself. No new units.

- #185 tan100 defined inconsistently
- #183 Fix typing error for weber quantity kind
- #184 Canonical form not described
- #189 Two concerns on syntax tree

## Version 2.0.1

## Version 2.0

- Emergency minor release 2.0.1 on 13-NOV-2015 to fix the exponent of Planck's constant. #175
- ucum-essence.xml had elements in no name space. This was obviously a bug. It was resolved, not an emergency, but would have been more difficult to hold this minor fix back until 2.1 #157

## Version 1.9

### New units

tex | 1 | g/km | metric | tex |

[den] | 1 | g/9/km | nonmetric | Denier |

[anti'Xa'U] | 1 | 1 | nonmetric | arbitrary anti factor Xa unit |

[EID_50] | 1 | 1 | nonmetric | arbitrary 50% embryo infectious dose |

[Amb'a'1'U] | 1 | 1 | nonmetric | arbitrary allergen unit for Ambrosia artemisiifolia |

[Lf] | 1 | 1 | nonmetric | arbitrary Limit of flocculation |

[D'ag'U] | 1 | 1 | nonmetric | arbitrary D-antigen unit |

[FEU] | 1 | 1 | nonmetric | arbitrary fibrinogen equivalent unit |

[ELU] | 1 | 1 | nonmetric | arbitrary ELISA unit |

[EU] | 1 | 1 | nonmetric | arbitrary Ehrlich unit |

[foz_m] | 30 | mL | nonmetric | metric fluid ounce |

[cup_m] | 240 | mL | nonmetric | metric cup |

[tsp_m] | 5 | mL | nonmetric | metric teaspoon |

[tbs_m] | 15 | mL | nonmetric | metric tablespoon |

[oz_m] | 28 | g | nonmetric | metric ounce |

[degR] | 5 | K/9 | nonmetric | degree Rankine |

### Changed Units

#### Exact Constants

The following units are modified to turn constants which were stated of limited precision to exact. This is indicated by removing the decimal point from the number. If a number has a decimal point, it is considered having this number of significant digits, hence limited precision. If there is no decimal point (and magnitude adjusted in the exponent) it is considered exact.

[g] | 980665e-5 (was: 9.80665) | m/s2 | metric | standard acceleration of free fall |

m[H2O] | 980665e-5 (was 9.80665) | kPa | metric | meter of water column |

Ci | 37e9 (was: 3.7e10) | Bq | metric | Curie |

[car_m] | 2e-1 (was: 0.2) | g | nonmetric | metric carat |

#### Corrected Constants

[Ch] | 1 | mm/3 (was: mm/[pi]) | nonmetric | Charrière |

AU | 149597.870691 | Mm | nonmetric | astronomic unit |

[drp] | 1 | ml/20 (was: ml/12) | nonmetric | drop |

## Version 1.8.2

The major change of this release is the establishment of a class of "arbitrary units" which are no longer simply dimensionless. This is to protect the false assumption that one could convert measurement values expressed in some arbitrary unit into one in another arbitrary or dimensionless units.

## Version 1.8

New units:

[wood'U] | 1 | mm[Hg].min/L | nonmetric | Wood unit |

[IU] | 1 | [iU] | metric | arbitrary international unit |

[BAU] | 1 | 1 | nonmetric | arbitrary bioequivalent allergen unit |

[AU] | 1 | 1 | nonmetric | arbitrary allergen unit |

[PNU] | 1 | 1 | nonmetric | arbitrary protein nitrogen unit |

B[10.nV] | * | 2lg(10 nV) | metric | bel 10 nanovolt |