XJNick

Hi, I built this voltmeter circuit, but have a question regarding the power supply for it. I notice the schematics show ground symbols in addition to + and - supply voltage. So would these indicate true earth grounds? I ask because I want to be able to use a digital voltmeter like this in my car, where (I believe) there would be no true ground? Is there any way to get around this? I was able to get the 7805 to produce 5.0 volts when it's ground leg is attached to the - terminal of the 12 volt battery i'm using (and its V. in leg attached to the +12 volt battery terminal). I doubt this would work for the 7905 to make a -5volt supply though? ??? Thanks -Nick