The NIST high-purity primary standard reagent SRMs are the benchmark for a wide variety of acidimetric and oxidation-reduction titrations. This suite of SRMs includes SRM 84k Potassium Hydrogen Phthalate, SRM 350b Benzoic Acid, and SRM 973 Boric Acid, each used as a standard acid. SRM 723d Tris(hydroxymethylamino)methane and SRM 351a Sodium Carbonate are used as standard bases. SRM 999b Potassium Chloride is used in argentimetric titrations and as a K and Cl standard. SRM 136f Potassium Dichromate is a widely used oxidimetric standard reagent. Probably the most critical use for SRM 136f is in the assay of uranium in nuclear safeguards analyses. Here, a low uncertainty is necessary in exposing diversion, loss, or theft of fissionable material.