VDC step down-step up voltage selector design

[Sourcetest]

Please help an environmental guy with basic electrical knowledge build a project. I am building a dilution system for an odor study utilizing two mass flow controllers which require 5vdc for full scale. Mass flow controllers have a linear output according to the supplied vdc input along their full scale or FS.
I would like to build one board where i can put a 11 point switch or 11 push bottons to allow 0-100% in 10% or 0.5vdc increments.

But if say one mfc is running at 1vdc the other should be at 4vdc. I know there is a simple way to accomplish this and i am over thinking it. Any help will be appreciated.

 

[FvM]

So you are building an electronic gas divider. I presume you know how to make a 10% step voltage divider with 10 equal resistors.For the 5V - x operation, you need an opereational amplifier in a substractor circuit.

 

[Sourcetest]

Yes i am making a gas divider. I have an odor study which will require us to calibrate on various gases at varying levels. I do know what an op amp is and resistors but i am unsure the exact arrangement required however. Please understand, while i love electronics and wish i knew more, but environmental is my profession.

 

[FvM]

A basic OP differential amplifier with 4 equal resistors works as a substractor y = x1 - x2

https://en.wikipedia.org/wiki/File:Op-Amp_Differential_Amplifier.svg