**Defined in theory: Physical-quantities****Source code: physical-quantities.lisp**

**Documentation:**identity-dimension is the identity element for the * operator over physical-dimensions. That means that the product of identity-dimension and any other dimension is that other dimension. Identity-dimension is the dimension of the so-called dimensionless quantities, including the real numbers.

**Instance-Of:**Physical-dimension

(Identity-Element-For Identity-Dimension * Physical-Dimension)