in the first box the microprocessor must rely upon some form of equation or table to relate theraw count value of the electrical measurement to the actual property of interest such astemperature pressure or flow. the principle form of this is usually established by themanufacturer but most HART instrument include commands to perform field adjustment. this often referred to as asensor trim the output of the first box is adigital representation of themprocess variable when you read the process variable using a communicator this is value thatyou see