Tolong jelaskan mengenai Kadar pertukaran dari Ngultrum Bhutan dalam bahasa melayu

Panish, Charles K: "Early Coinage of Bhutan". The American Numismatic Society, Museum Notes 17, New York 1971, p. 247-254 and plates XLVII-XLVIII.

Rhodes, Nicholas:The Coinage of Bhutan. Oriental Numismatic Society, Information Sheet no 16, January 1977.

Rhodes, Nicholas: "Coinage in Bhutan".Journal of Bhutan Studies.. The Centre of Bhutan Studies, vol. 1, no. 1, Thimphu, Autumn, 1999, p. 84-113.

Rhodes, Nicholas: "The Monetisation of Bhutan". Journal of Bhutan Studies.. The Centre of Bhutan Studies, vol. 2, no. 1, Thimphu, Winter 2000, p. 85-103.