Maybe I am a bit of an outlier when it comes to tradition; but, I avoided the whole shunt thing by not using an ammeter. An ammeter, in my opinion, tells a person something (which way the current is flowing and how much) but it does not provide certain useful information like a voltmeter (overvoltage/undervoltage). One of the destructive failure modes, to other equipment, of a regulator is not controlling overvoltage.....a 12 volt system running at 16 V rather than 14 like it should will show a charge on an ammeter like everything is hunky-dory, but it will fry a battery. A voltmeter is a simple hot wire to the charging system and a ground. I think both gauges provide information, just that the voltmeter will be instant and maybe provide a little more direct information. But that's just me