This chapter documents the components that read and/or write the neutron spin state \((s_x,s_y,s_z)\): polarisation setting/analysis, polarising monochromators/mirrors/guides, and magnetic-field regions implementing spin precession. The underlying formalism – the polarisation vector, the master polarised-scattering equations, the \(F_N\)/\(F_M\) treatment of polarising monochromators and guides, the spin-precession algorithm, and the available magnetic field functions – is described in full in the Polarisation chapter (15.14); this chapter focuses on the component parameter tables themselves. See also section 8.1 above for Monochromator_pol.