Portable modular unit for inspecting in a timepiece the presence of a lubricating agent, or of an epilame, having fluorescent markers, from an excitation luminous flux of white light, said portable modular unit comprising an optical housing, forming a first module, a portable white light source emitting an excitation luminous flux, forming a second module, a portable magnifying device, forming a third module; said optical housing supporting: - an excitation filter configured to select in the excitation luminous flux of said portable white light source, the wavelength range suitable for the excitation of the fluorescent markers of the lubricating agent or of the epilame to be inspected, and to transmit a filtered excitation luminous flux; - a dichroic filter configured to reflect said filtered excitation luminous flux and to orient said filtered excitation luminous flux in the direction of an inspection opening capable of being positioned opposite said timepiece, said dichroic filter also being configured to allow a reflection luminous flux emitted by said timepiece under excitation of said filtered excitation luminous flux to pass through; - an emission filter configured to filter the reflection luminous flux and transmit a fluorescence luminous flux corresponding to the fluorescence of the fluorescent markers of said lubricating agent or of the epilame to be inspected; said optical housing comprising: - a first mounting interface for removably mounting said portable white light source on the optical housing, the first mounting interface being an interface of the female type comprising a first cavity, of circular cylindrical shape, in such a way as to correspond to the circular shape of the portable white light source formed by a torch or a penlight, the first mounting interface being configured so that said excitation luminous flux emitted by said portable white light source is directed in the direction of said excitation filter; - a second mounting interface for removably mounting said portable magnifying device on the optical housing, said second mounting interface being configured so that said magnifying device is opposite the inspection opening. said optical housing supporting: - an excitation filter configured to select in the excitation luminous flux of said portable white light source, the wavelength range suitable for the excitation of the fluorescent markers of the lubricating agent or of the epilame to be inspected, and to transmit a filtered excitation luminous flux; - a dichroic filter configured to reflect said filtered excitation luminous flux and to orient said filtered excitation luminous flux in the direction of an inspection opening capable of being positioned opposite said timepiece, said dichroic filter also being configured to allow a reflection luminous flux emitted by said timepiece under excitation of said filtered excitation luminous flux to pass through; - an emission filter configured to filter the reflection luminous flux and transmit a fluorescence luminous flux corresponding to the fluorescence of the fluorescent markers of said lubricating agent or of the epilame to be inspected; - an excitation filter configured to select in the excitation luminous flux of said portable white light source, the wavelength range suitable for the excitation of the fluorescent markers of the lubricating agent or of the epilame to be inspected, and to transmit a filtered excitation luminous flux; - a dichroic filter configured to reflect said filtered excitation luminous flux and to orient said filtered excitation luminous flux in the direction of an inspection opening capable of being positioned opposite said timepiece, said dichroic filter also being configured to allow a reflection luminous flux emitted by said timepiece under excitation of said filtered excitation luminous flux to pass through; - an emission filter configured to filter the reflection luminous flux and transmit a fluorescence luminous flux corresponding to the fluorescence of the fluorescent markers of said lubricating agent or of the epilame to be inspected; said optical housing comprising: - a first mounting interface for removably mounting said portable white light source on the optical housing, the first mounting interface being an interface of the female type comprising a first cavity, of circular cylindrical shape, in such a way as to correspond to the circular shape of the portable white light source formed by a torch or a penlight, the first mounting interface being configured so that said excitation luminous flux emitted by said portable white light source is directed in the direction of said excitation filter; - a second mounting interface for removably mounting said portable magnifying device on the optical housing, said second mounting interface being configured so that said magnifying device is opposite the inspection opening. - a first mounting interface for removably mounting said portable white light source on the optical housing, the first mounting interface being an interface of the female type comprising a first cavity, of circular cylindrical shape, in such a way as to correspond to the circular shape of the portable white light source formed by a torch or a penlight, the first mounting interface being configured so that said excitation luminous flux emitted by said portable white light source is directed in the direction of said excitation filter; - a second mounting interface for removably mounting said portable magnifying device on the optical housing, said second mounting interface being configured so that said magnifying device is opposite the inspection opening.