Voltage gauge, not amp gauge.
You need to get a handheld voltage meter.
Check battery with engine off, should be 12.4-12.9volts
Voltage at battery should now be 14.5 to 14.9, recharging battery after starting
After 3 minutes of idling voltage should drop down to 13.5-13.9volts, keeps battery charged but won't ruin it.
Now with engine still idling, turn on head lights and blower to high, voltage should drop then come back up to 13.5-13.9volt area.
Just FYI, alternator running above 15volts means a problem, hopefully with your dash board gauge, which is why you need to test with a meter.
Above 15volts will ruin the battery and can damage electronics.
Voltage regulator in the alternator sets minimum and maximum voltages