The US schedule carves out seismographs into their own 10-digit line (9015806000), separate from other geophysical instruments not elsewhere specified (9015808040) and the general residual surveying line (9015808080). This distinction matters because the tariff treatment and statistical reporting differ. An instrument that records seismic waves for earthquake monitoring or oil exploration should be classified as a seismograph; broader geophysical survey tools such as gravimeters or magnetometers fall under the geophysical NESOI line.

Multi-function instruments — for example, a unit that integrates GPS positioning with hydrographic depth-sounding — require the importer to identify the component that imparts the article's essential character for classification. CBP may request technical specifications, manufacturer datasheets, or a binding ruling to confirm the correct 10-digit line. Importers should also verify whether the instrument is subject to export controls in the country of origin, as some geophysical instruments have dual-use implications.