Fuel and oil cleanliness is measured by calculating the total number of contaminants found in at least one milliliter of fluid 

The total number of contaminants are then broken down into three different size categories and are written as a three numbered measurement. I.E. *18/*16/*13. This is known as an ISO code.

Lab analysis can show ISO codes and informs you of your general cleanliness and if you have any abnormal contamination in a given set of fluid. (Fuel, engine oil, hydraulics, etc.)