The MDL in RoHS test report is the lowest detection limit of the substance by equipment, that is, the lowest content that can be detected. When the content of this substance in the sample is below this limit, the equipment can't detect it, which is reflected in the report. Similarly, when the report shows that this substance is ND, it does not mean that the sample must not contain this substance, but it may contain it, but the content is so low that the equipment cannot detect it.
MDL is the abbreviation of minimum detection limit, which is the minimum value that can be measured by a machine. The smallest scale equivalent to a ruler is 1 mm.