Urea - DEF Refractometer Tester is functional as an ideal instrument suited for testing DEF. This is useful to prevent the utilization of fluid at expected values. It has the capacity to accurately and quickly check the samples. In addition, it measures the urea concentration. Urea - DEF Refractometer Tester The refracto meter is a functional as a portable precision optical instrument that can perform the diesel exhaust fluid concentration very well. It works in a quick as well as easy way and offers accurate readings.