Train jewels must be perfectly clean before any lubrication is applied. It is preferable for lubricants to be applied directly to the oil cup after installing the bridge, but they can be applied directly to the pivot of the component before installing it when applying lubricant to the oil cup is not practical or there is a high risk for oil to be applied in areas where it critically should not be. Both methods of applying oil must be precisely and cleanly performed. When the component is installed, the oil should fill the space between the jewel and the pivot and extend out into the oil cup with sufficient reserve to last the full service interval. In many watches this means the oil will extend to a height of about half the depth of the oil cup. Too little oil will cause premature wear of the component over the service interval, and too much oil introduces the possibility that oil will contact the bridge and be drawn away from the pivot, run down the arbor to the pinion, or contaminate nearby components. No oil should be present on the flat top of the jewel, and there must be no contaminants on the jewel or in the oil.
To assess the quantity and condition of oil, it is important to move the watch movement around so that the light is reflected in different directions. This will help you see where the oil is located and if it is clean. Moving the wheel and pivot as though testing for endshake or side shake will force the oil to move, making it easier to see and assess the quantity of oil.