Need to convert a two wire 0 to 15 volt dc analog panel meter to read 0 to 30 volt dc how can I do this and what parts will I need?

PUT A MULTIPLIER RESISTOR IN SERIES WITH THE METER AND SOURCE. RESEARCH 'METER SHUNTS AND MULTIPLIER CIRCUITS', IT TAKES ONLY ONE SMALL RESISTOR.....(OR IF YOU HAVE EXTRA METERS, PUT TWO OF THEM IN SERIES WITH THE LOAD AND SOURCE; THEN ADD THE TWO METER READINGS.)