# gal, Gal (unit)
This page documents an [OPTIMADE](https://www.optimade.org/) [Unit Definition](https://schemas.optimade.org/#definitions). See [https://schemas.optimade.org/](https://schemas.optimade.org/) for more information.
**ID: [`https://schemas.optimade.org/defs/v1.2/units/si/general/gal`](https://schemas.optimade.org/defs/v1.2/units/si/general/gal.md)**
**Definition name:** `gal`
**Unit name:** gal
**Latin symbol:** Gal
**Display symbol:** Gal
**Description:** A unit of acceleration equal to 1 centimeter per second squared (1 cm/s²), using the current, or one of the historical, definitions of the SI units.
The gal unit appears in the International System of Units (SI), 1st ed. (1970) defined as "1 Gal = 1 cm/s² = 10⁻² m/s²" with the footnote "The gal is a special unit of acceleration employed in geodesy and geophysics to express acceleration due to gravity."
- The International System of Units (SI), 1st ed. (1970) categorizes the unit as "units in use temporarily".
- The International System of Units (SI), 7th ed. (1998) changes the categorization to "derived CGS units with special names".
- The International System of Units (SI), 9th ed. (2019) moves the unit definition to the margin aside the table for Non-SI units accepted for use with the SI units.
It is not clear how to interpret the categorization intended with this placement of the unit.
The galileo unit was implicitly redefined via the redefinition of the metre at the 17th CGPM meeting (1983), resolution 1.
This is a generalized definition taken to reference the current, or one of the historical, SI unit definitions.
This 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.
**Resources:**
- [Definition in the International System of Units (SI), 1st Edition](https://www.bipm.org/en/publications/si-brochure)
- [Redefinition of the metre at the 17th CGPM meeting (1983), resolution 1](https://www.bipm.org/en/committees/cg/cgpm/17-1983/resolution-1)
- [Wikipedia article describing the unit](https://en.wikipedia.org/wiki/Gal_(unit))
**Compatibility:** (other definitions that are covered by the above definition)
- [`https://schemas.optimade.org/defs/v1.2/units/si/1970/temporary/gal`](https://schemas.optimade.org/defs/v1.2/units/si/1970/temporary/gal.md)
- [`https://schemas.optimade.org/defs/v1.2/units/si/1983/temporary/gal`](https://schemas.optimade.org/defs/v1.2/units/si/1983/temporary/gal.md)
**Formats:** [[JSON](gal.json)] [[MD](gal.md)]
**JSON definition:**
``` json
{
"$id": "https://schemas.optimade.org/defs/v1.2/units/si/general/gal",
"$schema": "https://schemas.optimade.org/meta/v1.2/optimade/physical_unit_definition.json",
"title": "gal",
"symbol": "Gal",
"display-symbol": "Gal",
"description": "A unit of acceleration equal to 1 centimeter per second squared (1 cm/s\u00b2), using the current, or one of the historical, definitions of the SI units.\n\nThe gal unit appears in the International System of Units (SI), 1st ed. (1970) defined as \"1 Gal = 1 cm/s\u00b2 = 10\u207b\u00b2 m/s\u00b2\" with the footnote \"The gal is a special unit of acceleration employed in geodesy and geophysics to express acceleration due to gravity.\"\n\n- The International System of Units (SI), 1st ed. (1970) categorizes the unit as \"units in use temporarily\".\n- The International System of Units (SI), 7th ed. (1998) changes the categorization to \"derived CGS units with special names\".\n- The International System of Units (SI), 9th ed. (2019) moves the unit definition to the margin aside the table for Non-SI units accepted for use with the SI units.\n It is not clear how to interpret the categorization intended with this placement of the unit.\n\nThe galileo unit was implicitly redefined via the redefinition of the metre at the 17th CGPM meeting (1983), resolution 1.\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/gal",
"https://schemas.optimade.org/defs/v1.2/units/si/1983/temporary/gal"
],
"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/Gal_(unit)"
}
],
"defining-relation": {
"base-units": [
{
"symbol": "m",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/general/metre"
},
{
"symbol": "s",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/general/second"
}
],
"base-units-expression": "m*s^-2",
"scale": {
"exponent": -2
}
},
"x-optimade-definition": {
"label": "gal_si_general",
"kind": "unit",
"format": "1.2",
"version": "1.2.0",
"name": "gal"
}
}
```