Viscosity sensors measure the thickness of fluids, but they do not directly indicate grease levels in gear systems. The discussion highlights the distinction between grease and lubricating oil, emphasizing that traditional grease is often a semi-solid, while oil is a freely-flowing fluid. Various methods exist to determine lubricant levels and viscosity, but the effectiveness of these methods can depend on specific design factors like gearbox dimensions and gear placement. Clarification on the type of viscosity sensor and its application is necessary for accurate recommendations. Understanding these distinctions is crucial for selecting the appropriate measurement approach for grease in gear systems.