Good site by picture alone you can have a book,with other info from legislation to circulation,to paper use to color coding in banknotes to banknotes back by precious metal to full fiat,what will happen if the Philippine go back to precious metal is other banknote redeemable in certain grain of silver and gold from specimen to release in circulation studying variety in note but have actual sample,just like proof to business strike.other even weighing banknote,certain amount or pieces can be printed in sheet of security paper or certain weight for certain ratio?just a comment