Pracha Siwawetkul. (1985) A study on the design and construction of the inexpensive digital pH meter for portable use. Mahidol University,:ม.ป.ท.Pracha Siwawetkul. 1985. A study on the design and construction of the inexpensive digital pH meter for portable use. ม.ป.ท.:Mahidol University,;Pracha Siwawetkul. A study on the design and construction of the inexpensive digital pH meter for portable use. ม.ป.ท.:Mahidol University, 1985. Print.