A physical constant is a quantity whose value is independent of the particular experiment within a stated physical theory and regime. Examples include the speed of light in vacuum and Planck constant. A numerical value depends on the units of measurement; a dimensionless constant avoids that dependence.
Some constants have exact numerical values by the definition of the International System of Units. Others, such as the fine-structure constant, remain measured quantities with experimental uncertainty. Exact unit-defining values do not imply that every realization of those units is exact.[ref]
The International System of Units (SI), ninth edition, SI Brochure. §2.2, defining constants and unit definitions
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A physical constant is a quantity with a fixed value that does not change in time or space. These constants are fundamental in the laws of physics and are used to describe the properties of the universe. Examples of physical constants include: 1. **Speed of Light (c)** - Approximately \(299,792,458\) meters per second in a vacuum. 2. **Gravitational Constant (G)** - Approximately \(6.
