is there a body or organization that controls it?
Yes - General Conference on Weights and Measures (CGPM)
International System of Units
The SI was established and is maintained by the General Conference on Weights and Measures (CGPM). In practice, the CGPM follows the recommendations of the Consultative Committee for Units (CCU), which is the actual body conducting technical deliberations concerning new scientific and technological developments related to the definition of units and the SI. The CCU reports to the International Committee for Weights and Measures (CIPM), which, in turn, reports to the CGPM. See below for more details.

All the decisions and recommendations concerning units are collected in a brochure called "The International System of Units (SI)", which is published by the International Bureau of Weights and Measures (BIPM) and periodically updated.
having all units in atomic standards is more useful. explain UNANSWERABLE
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International System of Units [SEP] Controlling body
The SI was established and is maintained by the General Conference on Weights and Measures (CGPM). In practice, the CGPM follows the recommendations of the Consultative Committee for Units (CCU), which is the actual body conducting technical deliberations concerning new scientific and technological developments related to the definition of units and the SI. The CCU reports to the International Committee for Weights and Measures (CIPM), which, in turn, reports to the CGPM. See below for more details. All the decisions and recommendations concerning units are collected in a brochure called "The International System of Units (SI)", which is published by the International Bureau of Weights and Measures (BIPM) and periodically updated.