The speaker was Ir. Dr. Francis SY Wong (Standards and Calibration Laboratory (SCL), ITC, HKSAR). He is the Engineer-in-charge of the Dimension Laboratory, SCL. In the beginning, Dr. Wong briefed the fundamental concepts of surface roughness and drawn the diagram for explanation.
Ra is the arithmetic average of the roughness and explained in the following diagram.
Then Dr. Wong showed the standard of surface roughness. You could compare different roughness by touching the samples.
Lastly, the measurement result by surface roughness meter was demonstrated.
Institute of Measurement and Control (Hong Kong Section) - http://www.instmc.org.hk/
Standards and Calibration Laboratory - Dimension - http://www.itc.gov.hk/en/quality/scl/em/em6.htm