Measurement instrument, measurement device, measurement system, and measurement method

A measurement method using a measurement instrument, the measurement instrument including:

• a cylindrical cell that stores a measurement fluid;
• a drive mechanism that rotates the cell about a central axis;
• a first light source that is arranged outside the cell and irradiates the measurement fluid with first inspection light;
• a second light source that is arranged outside the cell and at a position different from the first light source in a rotation direction of the cell, and irradiates the measurement fluid with second inspection light;
• a detector that is arranged outside the cell and detects transmitted light of the first inspection light transmitted through the measurement fluid and scattered light of the second inspection light scattered by the measurement fluid;
• and
• a cleaning mechanism that is arranged inside the cell and comes into contact with and clean an inner peripheral surface of the cell, wherein
• the cleaning mechanism includes a first cleaning mechanism arranged between the second light source and the detector.