Oakton waterproof DO 450 and pH/DO 450 optical meters from Cole-Parmer have no membrane or electrolyte to replace, no incoming flow requirement and no hydrogen sulfide interference. The meters also feature short response time, minimal drift and minimal maintenance. Up to 500 data sets can be stored and downloaded with USB or RS-232 cable. The DO 450 meter has manual barometric pressure and salinity corrections. The pH/DO meter offers six-point calibration. 800/323-4340; www.coleparmer.com.