Problem with FC105 and FC106

This is the scenario I want to develop in Step7 by LAD programming: 

In the manufacturing process, an oil pumps is responsible for transferring oil to the filler line. One sensor is also installed on the line to measure the oil concentration. An electric valve is also provided and Its function is to control the oil outlet and this valve is embedded in 4 to 20 mA. Design the line so that, base on the "oil concentration-motor speed" ratio, the valve opens at the end of the line so that the oil outlet pressure is always at 8 Bars. (pump is 0 to 10 volts and a pressure sensor of 4 to 20 mA is provided at the end of the line). 

It is obvious that I can use FC42 to maintain 8 Bars at the valve and in order to scale input of motor pump and the sensor responsile for oil concentration I need FC105 module. However, it is confusing that if I ever need a FC106 module to unscale the desire ratio. If so, I don't know how exactly implement the scenario.

Any help you can give would be appreciated. 

Maybe this link can help you:

How can you standardize and destandardize analog values with STEP 7 V5.5?