Why does the viscosity of a Non-Newtonian fluid change with time from start of measurement? [Viscometers] [SV10/100]

Viscosity change of a Non-Newtonian fluid appears as its physical structure is changed or damaged when stirred, beaten or pressed with stress. In measurement with the SV Series, viscosity usually decreases in the beginning as the vibration starts breaking the fluid structure around the sensor plates, but then stabilizes after a period time. In case of the rotational viscometer it causes greater damage to fluid structure and takes longer to stabilize the result in measurement than the SV Series does.