milliseimensseinä

The milliseimensseinä (often abbreviated as mSs) is a unit of magnetic flux density used in the context of magnetic materials and electromagnetic measurements, particularly in Finnish scientific and industrial literature. It is derived from the SI unit of magnetic flux density, the tesla (T), and represents one-thousandth of a seimensseinä (Ss), a non-standard unit historically used in Finland.

The seimensseinä itself was defined as the magnetic flux density that produces a magnetic field strength of one ampere per meter (A/m) in a material with a magnetic permeability of 4π × 10⁻⁷ henries per meter (H/m), which is the permeability of free space (μ₀). This unit was introduced in Finland to simplify calculations in electromagnetism, particularly in engineering and physics contexts where Gaussian units were less common.

The milliseimensseinä is thus equal to 10⁻³ Ss, which corresponds to approximately 4π × 10⁻¹⁰ tesla (T). This unit is rarely encountered in international scientific literature but remains relevant in certain Finnish technical and research publications, particularly in older documents or specialized fields such as magnetism studies in Finnish universities or industries.

While the tesla remains the standard SI unit for magnetic flux density, the milliseimensseinä persists as a legacy unit in some localized applications. Its use reflects historical conventions in Finnish scientific communication rather than any fundamental advantage over SI units. Modern practice generally favors the tesla or its submultiples (e.g., microtesla, μT) for consistency with international standards.