Oakton's TDS Testr 11 measures TDS (or conductivity) and comes complete with Automatic Temperature Compensation (ATC) and is waterproof and dustproof. Reuse the meter body many times without losing waterproof and dustproof protection. Replaces TDSTestr Low (no. WD-35661-14) and TDSTestr High (no. WD-35661-24), with each separate scale selectable on a large display screen.