What other options are there for y-axis units other than concentration?

There are three y-axis display options for histograms: Concentration, Particle Count, % Population.

In the 'Histogram Settings' section, the display option can be manually selected. Histograms will default to display the y-axis as: 

• Concentration when all samples being viewed contain a concentration value. 
• % Population when a concentration is not available for all viewed samples.

This option can be turned off by unticking the 'Default to concentration where possible' check box.