YSI Truline 400387 Combination Calcium Electrode, BNC Connector, 1m Cable. The TruLine series of laboratory ISEs consists of 15 electrodes that have an integrated reference, eliminating the need to have a separate reference half-cell. Each TruLine ISE has a refillable double-junction reference, resulting in a long electrode life and exceptional measurement reliability. TruLine ISEs can be connected to any ISE instrument featuring BNC connection, including the YSI 1320. Reference/electrode fill solution, ionic strength adjustor, and small bottle of standard are included with each ISE.