Length precision (property)

{
    "$id": "https://schemas.httk.org/defs/v0.1/properties/core/length_precision",
    "$schema": "https://schemas.optimade.org/meta/v1.2/optimade/property_definition.json",
    "title": "Length precision",
    "x-optimade-type": "float",
    "x-optimade-definition": {
        "label": "length_precision_core",
        "kind": "property",
        "version": "0.1.1",
        "format": "1.3",
        "name": "length_precision"
    },
    "type": [
        "number",
        "null"
    ],
    "description": "The absolute precision of a stated length, in \u00e5ngstr\u00f6m.\n\nThis describes how precisely a length was *stated* by the source it came from, rather\nthan the precision of the number as stored. A cell edge written `5.6402` claims a\nprecision of about `0.0001` \u00e5ngstr\u00f6m; one written `5.6402(3)` claims `0.0003`, since an\nexplicitly stated uncertainty overrides what the digits alone would imply.\n\n**Requirements/Conventions**:\n\n- The value is an **absolute** bound on the deviation from the intended value, in the same\n  units as the length it describes, and is neither a relative precision nor a count of\n  significant figures.\n- Where a set of lengths is described by a single value, it SHOULD be the **coarsest**\n  precision among them.\n- Where a source states both a number of digits and an explicit standard uncertainty, the\n  value SHOULD be the larger of the two, that being the weaker and therefore the safer\n  claim.\n- Precisions of quantities in other units, such as the angles of a unit cell, MUST NOT be\n  combined into this value; they are not lengths and combining them would produce a\n  quantity in no units at all.\n- The value MUST be strictly positive. A value of zero would assert exactness, which is a\n  different claim; `null` MUST be used where the precision is unknown.",
    "examples": [
        0.0001,
        0.0003
    ],
    "x-optimade-unit": "angstrom",
    "x-optimade-unit-definitions": [
        {
            "$id": "https://schemas.optimade.org/defs/v1.2/units/si/general/angstrom",
            "title": "\u00e5ngstr\u00f6m",
            "symbol": "angstrom",
            "display-symbol": "\u00c5",
            "description": "A unit of length equal to 10\u207b\u00b9\u2070 meter, using the current, or one of the historical, definitions of the SI units.\n\nThe \u00e5ngstr\u00f6m unit appears in the International System of Units (SI), 1st ed. (1970) defined as \"1 \u00c5 = 0.1 nm = 10\u207b\u00b9\u2070 m\".\n\nThe \u00e5ngstr\u00f6m unit was implicitly redefined via the redefinition of the metre at the 17th CGPM meeting (1983), resolution 1.\n\n- The International System of Units (SI), 1st ed. (1970) categorizes the unit as \"temporarily admitted\" for use with the SI units.\n- The International System of Units (SI), 7th ed. (1998) changes the categorization to \"Other non-SI units currently accepted for use with the International System.\"\n- The International System of Units (SI), 8th ed. (2006) changes the categorization to \"Other non-SI units\" and adds as a clarifying footnote \"The \u00e5ngstr\u00f6m is widely used by x-ray crystallographers and structural chemists because all chemical bonds lie in the range 1 to 3 \u00e5ngstr\u00f6ms. However it has no official sanction from the CIPM or the CGPM.\"\n- The \u00e5ngstr\u00f6m is omitted in the International System of Units (SI), 9th Edition (2019).\n\nThis is a generalized definition taken to reference the current, or one of the historical, SI unit definitions.\nThis definition is intended for situations when it is not possible to be more precise, e.g., in contexts where data have been collected that uses different historical SI definitions.",
            "compatibility": [
                "https://schemas.optimade.org/defs/v1.2/units/si/1970/temporary/angstrom",
                "https://schemas.optimade.org/defs/v1.2/units/si/1983/temporary/angstrom"
            ],
            "resources": [
                {
                    "relation": "Definition in the International System of Units (SI), 1st Edition",
                    "resource-id": "https://www.bipm.org/en/publications/si-brochure"
                },
                {
                    "relation": "Redefinition of the metre at the 17th CGPM meeting (1983), resolution 1",
                    "resource-id": "https://www.bipm.org/en/committees/cg/cgpm/17-1983/resolution-1"
                },
                {
                    "relation": "Wikipedia article describing the unit",
                    "resource-id": "https://en.wikipedia.org/wiki/Angstrom"
                }
            ],
            "defining-relation": {
                "base-units": [
                    {
                        "symbol": "m",
                        "id": "https://schemas.optimade.org/defs/v1.2/units/si/general/metre"
                    }
                ],
                "base-units-expression": "m",
                "scale": {
                    "exponent": -10
                }
            },
            "x-optimade-definition": {
                "label": "angstrom_si_general",
                "kind": "unit",
                "format": "1.2",
                "version": "1.2.0",
                "name": "angstrom"
            }
        }
    ]
}