The top of the unit has a reset button which returns the gauge to its zero setting, but will instantly measure the current contamination of the filter when the engine is re-started.  All the guesswork of when filters are in need of changing is eliminated, NO numbers to read. When the YELLOW diaphram gets near the bottom RED area (10"hg. vacuum)  then.... Change the Filter. As long as the YELLOW indicator is in the GREEN  your good to GO. 

 

The R2D1 is 360* degree viewable from just about any angle and as the YELLOW diaphram indicator fills the gauge it can be seen from 9' away. No numbers to read, no little needles to look at, no having to look at it from one position. Simple, accurate, easy to install in any Diesel Fuel line that is on the suction side of the filter ( between the Filter and the Injector pump )

 

REMEMBER: The R2D1 can be read with the Engine or Pump OFF because it locks in position at the highest measured contamination level, which was measured when your engine was operating at full R.P.M. ( not just at idle ).  You can now check the condition of your Filters anytime you want;  when your engine and or engine room are cool. 

 

NOTE :  Most Diesel engines will begin to have running problems at 12 to15 hg. vacuum.  Know when your filter needs to be changed before your Engine shuts down.  BE SAFE NOT SORRY.  The 100 hour "change your filters rule"  has ruined more ENGINES AND FUEL PUMPS   because of a bad batch of Fuel that contaminated the filter in 8  hours and shut down the Engine and or wore out a fuel pump.  The reverse also holds  true.... knowing the condition of your Filter keeps you from throwing away a perfectly good filter ( it is not uncommon to get 300 to 500 hours out of a filter which has not been filtering contaminated  Fuel ). Also;  when you know you have clean fuel in your tanks, you can now  go to a lower number micron filter in your ENGINE FILTER, which will keep even more contaminates out of your INJECTOR PUMP.