= Material unaccounted for
<Material unaccounted for> is the difference between a recorded closing inventory and the measured physical inventory in <nuclear material accountancy>. With a consistent accounting period and material definition, $\mathrm{MUF}=B+R-S-E$, where $B$ is beginning inventory, $R$ receipts, $S$ removals and $E$ ending physical inventory.<IAEA Safeguards Glossary, 2001 Edition>[Entries6.42–6.43]{ref}
For instance, measured amounts $100+20-5-114$ leave an apparent difference of one mass unit. Interpretation requires <measurement uncertainty>: if the four measurement errors are independent, their variances add in the <variance> of the difference; correlated errors require covariance terms. A nonzero balance difference is therefore a measurement-and-reconciliation result that must be evaluated, rather than an automatic finding of missing physical material.<IAEA Safeguards Glossary, 2001 Edition>[Entry10.1, material balance evaluation]{ref}
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