Standard 209E remains today the most widely referenced standard in the world. There are several direct-reading instruments for measuring aerosol particle emissions. The CPC and differential mobility particle sizers, including the scanning mobility particle sizer and fast mobility particle sizer, can measure aerosol concentration; the diffusion charger and electric low pressure impactor can measure surface area; the size selective static sampler and tapered element oscillating microbalance can measure mass. For cleanrooms, the replacement standard is ISO 14644-1 and is meant to completely replace Federal Standard 209E. This ISO Standard can be found through the non-profit organization, Institute of Environmental Sciences and Technology (IEST). Each of these standards represents the maximum allowable number of particles in a unit of air. The typical unit is either cubic feet or cubic meters. The particle counts are always listed as cumulative. Liquid particle counters Liquid particle counters are used to determine the quality of the liquid passing through them. The size and number of particles can determine if the liquid is clean enough to be used for the designed application. Liquid particle counters can be used to test the quality of drinking water or cleaning solutions, or the cleanliness of power generation equipment, manufacturing parts, or injectable drugs. Liquid particle counters are also used to determine the cleanliness level of hydraulic fluids and various other systems including (engines, gears and compressors), the reason being that 75-80% of hydraulic breakdowns can be attributed to contamination. There are various types, installed on the equipment, operated in a laboratory as part of an oil analysis programme. or portable units that can be transported to site, e.g., a construction site, and then used on the machine, e.g., a bulldozer, to determine fluid cleanliness. By determining and monitoring these levels, and following a proactive or predictive maintenance program, the user can reduce hydraulic failures, increase uptime and machine availability, and to reduce oil consumption. They can also be used to assure that hydraulic fluids have been cleaned using filtration, to acceptable or target cleanliness levels. There are various standards in use in the hydraulic industry, of which ISO 4406:1999, NAS1638 and SAE AS 4059 are probably the most common. A typical hydraulic oil cleanliness to iso 4406 is 20/18/15. Solid particle counters Solid particle counters are used to measure dry particles for various industrial applications. One such application could be for the detection of particle size coming from a