a measurement system that can measure scattered light across a predetermined scatter angle is disclosed . the measurement system has a light source configured to provide light along a first axis . the measurement system has a lens system aligned along a second axis that has a first focus near the first axis and where the second axis is different than the first axis . the measurement system has a sensor located on the second axis at a second focus of the lens system and is configured to detect scattered light near the first focus . the measurement system has a mask located on the second axis and is configured to limit the light that reaches the sensor to a predetermined angle of scatter . the disclosed invention eliminates the need for multiple nephelometric measuring devices and also system verification devices in order to perform assay of the presents or absence or number of suspended particles in a media as well as verification of the systems ability to measure in compliance to required performance attributes .