second

of arc
Non-SI unit of plane angle: 1 ″ = 1 3600 ° = 4.848 137 ... × 10 −6 rad.
Source:
Green Book, 2nd ed., p. 113
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 991