Floats park at 1000 m depth and profile to the surface at programmed intervals, typically 5 to 10 days. Measurements are made as the float rises. Results are transmitted to orbiting satellites and then to shore when the float reaches the surface. The float then returns to its parking depth.

The Apex/ISUS float makes 60 measurements of nitrate and oxygen on each profile, and it measures temperature, salinity and pressure at 2 m intervals.

Battery life is sufficient for approximately 260 vertical profiles from 1000 m depth.

At a cycle time of 5 days, each float should profile for nearly four years.

The precision of the ISUS nitrate sensor is near 0.2 micromoles per liter (1 SD).

Absolute accuracy is about 0.5 micromoles per liter and can be improved by comparison to laboratory analyses to remove offsets.