This is an introduction to scaled information transmission signals (for example 4-20 mA, 3-15 psig, etc.), the actual sensed signals (like using orifice dP to infer flow rate, or temperature to infer composition), and reconstruction of the process variable of interest (like the flow rate or composition) from the scaled transmission signal.  This document is aimed at those who will be structuring the signal processing and calculations within data acquisition and control systems.  Readers should understand the interpretation and reconstruction of the Process Variable (PV) value from the transmission received in the control room, which is related to the Sensed Variable (SV) value, the actual measurement by the sensor.  And, readers should understand the associated issues associated with device calibration and digital discretization.