An assembly for feeding liquid to the inlet port of a liquid spraying device or spray gun. The method forms a non-transparent film on a transparent substrate and patterns an etch stop layer on the non-transparent film. In the preparation process, phenolic resin is dissolved in ethanol to give phenolic resin solution at concentration by 40\u02dc50 wt %; the oxidizer and reducer are pulverized, mixed, and then the phenolic resin solution is added to the mixed powder; next, the mixture is agitated, pelletized, dried, and shaped by pressure molding. A reference position for the absolute position of the magnetic linear encoder is set based on the reference position. The processor reads a partial snap shot image corresponding to a state after change from the first non-volatile memory and updates a corresponding portion of the entire snap shot image in the second non-volatile memory.