The process has two outputs y₁ (unmeasured) and y₂ (measured). The disturbance d affects the  process adversely that needs to be nullified by manipulating input u. The open loop model equations can be written as

	(V.35)
	(V.36)

In this case disturbance, which is usually not measured can be expressed in terms of two measurable quantities

(V.37)

And hence,

(V.38)

In other words, the variable y₁ is estimated through two measurable quantities y₂ and u . The rest is similar to regular feedback control. This control mechanism is termed as inferential control because here the controlled variable y₁ is never measured, rather it has been estimated through the inference drawn from measurement of other variables (y₂ and u in this case).