Single particle optical sizing (SPOS) is a particle size and count technique that provides results at high accuracy and resolution. Particles in liquid suspensions flow through a sensing zone illuminated by a laser beam. Each particle obscures and scatters the incident light source. With the AccuSizer LE-400 sensor, both the light obscuration and scattering are used to relate particle/ light interactions with particle size. Each particle is sized and counted one at a time, providing the concentration in particles/mL. The sample volume must also be accurate in order to generate accurate concentration data. This technical note presents data generated at customer request to prove the size, count, and volume accuracy of the AccuSizer SIS/Syringe Injection Sampler system.