Hierarchy classification:

1. top of the aat hierarchies
2. Objects Facet
3. Furnishings and Equipment (hierarchy name)
4. Measuring Devices (hierarchy name)
5. measuring devices (instruments)
6. [measuring devices for phenomena]
7. light measuring devices
8. light absorption measuring devices

Anotations

Scope note:

Photoelectric instruments equipped to measure the absorption of nearly monochromatic light in the visible range by a gas or liquid and so determine the concentration of the absorbing constituents in the gas or liquid.