${\Psi }_p={\displaystyle \underset{\text{C}}{\int }A\cdot }\text{d}r$

where dr is a vector line element

Note 1 to entry: For a closed curve C, the protoflux is equal to the magnetic flux Φ through an arbitrary surface S limited by the curve C

$\Phi ={\displaystyle \underset{\text{C}}{\oint }A\cdot }\text{d}r={\displaystyle \underset{\text{S}}{\int }B\cdot e_{\text{n}}}\text{d}A$

where B is the magnetic flux density and e_ndA a vector surface element of S (see IEV 121-11-21).

Note 2 to entry: The coherent SI unit of protoflux is weber, Wb = kg m² s⁻² A⁻¹.