Portable pH meter with accessories, ion selective electrode (ISE type), for fluoride measurement, by the Hach company, c. 1990. Model no.45400, serial no. 921000000784. Portable pH Meter, 1985-1995 1985-1995
Ion-selective electrode (ISE) meter, with a silver specific electrode, by Orion Research Inc., Beverly, Massachusetts, USA, 1997. Model 900200 with double reference power supply unit (not seen) and three bottles of electrode filling solutions. Ion-Selective Electrode (ISE) Meter, 1997 1997
