All notable changes to this project will be documented in this file.

Updates prior to v2.2 were ported from a legacy system and may not be formatted correctly.

This new version addresses a number of typographical errors, updates to constants, and adds two new units. Below is a summary of significant changes.

• Added [NTU] for Nephelometric Turbidity Unit
• Added [FNU] for Formazin Turbidity Unit
• Updated Newtonian constant of gravitation
• Updated proton mass
• Updated electron mass
• Updated Boltzmann constant
• Updated elementary charge
• Updated Avogadro's constant and associated values including atomic mass constant
• Updated vacuum electric permittivity

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

[http://unitsofmeasure.org/trac/query?status=closed&group=resolution&milestone=Version+2.0 List of Issues Resolved]

• 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

[http://unitsofmeasure.org/trac/query?status=closed&group=resolution&milestone=Revision+1.9 List of Issues Resolved]

||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

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

||[Ch] ||1 ||mm/3 (was: mm/[pi]) ||nonmetric ||Charrière ||AU || 149597.870''691'' || Mm || nonmetric || astronomic unit ||[drp] ||1 ||ml/20 (was: ml/12) ||nonmetric ||drop

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.

[http://unitsofmeasure.org/trac/query?status=closed&group=resolution&milestone=Revision+1.8 List of Issues Resolved]

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