A technical atmosphere (symbol: at) is a non-SI unit of pressure equal to one kilogram-force per square centimeter. The symbol 'at' clashes with that of the katal (symbol: 'kat'), the SI unit of catalytic activity; a kilotechnical atmosphere would have the symbol 'kat', indistinguishable from the symbol for the katal. It also clashes with that of the non-SI unit, the attotonne, but that unit would be more likely be rendered as the equivalent SI unit. Assay ton (abbreviation 'AT') is not a unit of measurement, but a standard quantity used in assaying ores of precious metals; it is \(29 1D6 \,grams\) (short assay ton) or \(32 2D3 \,grams\) (long assay ton), the amount which bears the same ratio to a milligram as a short or long ton bears to a troy ounce. In other words, the number of milligrams of a particular metal found in a sample of this size gives the number of troy ounces contained in a short or long ton of ore.