[dcb]

Can you declare press in global scope (right before loop) and modify:
void doDisplayInstantCurrent(){displayTripCombo('I','M' ,instant.mpg(),'S',instantmph(),'C','M',current.mp g(),'D',current.miles());}

to
void doDisplayInstantCurrent(){displayTripCombo('I','M' ,instant.mpg(),'S',instantmph(),'C','X',press,'D', current.miles());}


and see what you are getting for press in the lower left corner?