Scientific instruments: Identify what a fathometer measures. Consider typical marine and hydrographic applications when selecting the answer. Choose the correct measurement.

Given data

• Instrument: Fathometer.
• Use context: Marine navigation and sounding.

Concept/Approach
A fathometer is an echo-sounding device used to determine water depth, historically expressed in fathoms.

Reasoning
• It emits sound waves and measures the return time from the seabed. • Converting travel time with sound speed in water yields depth.

Verification
The name itself hints at "fathoms" (a unit of depth), confirming its purpose.

Common pitfalls
Confusing depth measurement with seismic intensity (seismograph) or wind speed (anemometer) or salinity (salinometer).

Final Answer
Depth of water (ocean/sea depth)