The present application provides a method of operating a particle size distribution measuring apparatus sample solution circulation system is constructed so as to reverse a flow direction of a sample solution which flows through a flow cell prior to a measurement of the particle size distribution within the sample solution. The first core layer includes a first surface connected to a power supply layer and a second surface corresponding to the first surface. The light guide plate and the distributed light source are arranged such that the light emitted by the distributed light source is edge-coupled into the light guide plate for being forward projected onto the display screen to illuminate the display screen from back. The network access module communicates with the server.