A variety of testers are available that use an amperometric two-electrode design. Versions of these meters include those for the measurement of high purity water and for water purified by reverse osmosis. Testers are available to display results in either conductivity or total dissolved solids. Some testers offer the option to switch modes. Many of the testers use graphite sensors for the electrode to reduce polarization effects and have an exposed temperature probe for fast response when compensating for temperature variations.