1. n. 
The smallest change in a measurement that can be recorded by an instrument.
2. n. 
In matrix stimulation, a characteristic of rock that indicates the degree of reaction between the rock minerals and a given treating fluid. A formation is described as sensitive if a given stimulating fluid damages the formation. The detrimental reactions include disaggregation and collapse of the matrix, release of fines or formation of precipitates. Sensitivity depends on the overall reactivity of the formation minerals with the fluid; reactivity depends on the structure of the rock and the distribution of minerals within the rock. Sandstone sensitivity also depends on permeability; low-permeability formations are normally more sensitive than high-permeability sandstones for a given mineralogy because certain types of damage, such as formation of precipitates, are more harmful in small pore throats (as in low-permeability formations).