analogRead-ing Potentiometer Values in void setup()
You presumably know that:  The easiest and usual way to read a potentiometer is to connect the "track" between V_pot (often = Vcc) and ground and to connect the pot "wiper" to an analog input pin. You then use analogRead(Ax) to read the pot value in the range 0-255.  

The use of analogRead() is valid in setup.

However a more "real" method would be to have a "flag" variable that indicates that the speedo initialisation code has or hasn't been run.
Set this flag to false in setup, detect and action it in loop and then set the flag to true so that the code is not repeatedly actioned. 



eg

void setup()
{

...
boolean initialised = false ;
...
}

void loop()
{
if (initialised == false) {
// initialise speedo
//  ....
   initialised = true;
}

...

} // end of loop()

}