This is a DEF or Diesel Exhaust Fluid Refractometer made by OTC Tools.
The refractometer is a portable precision optical instrument
used for measuring the diesel exhaust fluid concentration. This tool is
easy to use, simply place a liquid sample on the prism, and the light
passing through it is bent and the more concentrated the liquid the
more the light will bend. The refractometer contains a reticle or scale
that is enlarged through the eyepiece to measure this light and the
values on the scale have been established to evaluate the DEF
condition. EPA regulations require all diesel engines manufactured on
or after January 1 2010 to meet lowered NOx emissions standards. Most
heavy duty engine manufacturers have chosen to utilize SCR including
Detroit Diesel DD13 DD15 DD16 Cummins ISX line PACCAR and Volvo-Mack
