RAW K-RATIO
A k-ratio is the ratio of unknown intensity relative to a reference intensity. Several varieties of these are defined. The raw k-ratio is defined as the ratio of the unknown counts to the standard counts for an element. The intensities are usually corrected for beam drift, dead time, background and standard drift. See also unknown k-ratio, k-factor and ZAF. The expression is :
where
: 
is the unknown intensity for element A at λ
is the standard intensity for element A at λ
If the standard were a pure element, then the K(raw) would be a fraction less than or equal to 1, and very roughly equivalent to the elemental fraction in the unknown. This approximation has become known as "Castaing's first approximation", after the founder of EPMA.