6.A.6."Magnetometers", "magnetic gradiometers", "intrinsic magnetic gradiometers", underwater electric field sensors, "compensation systems", and specially designed components therefor, as follows:

Note 6.A.6. does not apply to instruments specially designed for fishery applications or biomagnetic measurements for medical diagnostics.
a. "Magnetometers" and subsystems, as follows:
1. "Magnetometers" using "superconductive" (SQUID) "technology" and having any of the following:
a. SQUID systems designed for stationary operation, without specially designed subsystems designed to reduce in-motion noise, and having a 'sensitivity' equal to or less (better) than 50 fT (rms) per square root Hz at a frequency of 1 Hz; or
b. SQUID systems having an in-motion-magnetometer 'sensitivity' less (better) than 20 pT (rms) per square root Hz at a frequency of 1 Hz and specially designed to reduce in-motion noise;
a. 2. "Magnetometers" using optically pumped or nuclear precession (proton/Overhauser) "technology" having a 'sensitivity' less (better) than 20 pT (rms) per square root Hz at a frequency of 1 Hz;
3. "Magnetometers" using fluxgate "technology" having a 'sensitivity' equal to or less (better) than 10 pT (rms) per square root Hz at a frequency of 1 Hz;
4. Induction coil "magnetometers" having a 'sensitivity' less (better) than any of the following:
a. 0.05 nT (rms)/square root Hz at frequencies of less than 1 Hz;
b. 1 x 10⁻³ nT (rms)/square root Hz at frequencies of 1 Hz or more but not exceeding 10 Hz; or
c. 1 x 10⁻⁴ nT (rms)/square root Hz at frequencies exceeding 10 Hz;
5. Fibre optic "magnetometers" having a 'sensitivity' less (better) than 1 nT (rms) per square root Hz;
b. Underwater electric field sensors having a 'sensitivity' less (better) than 8 nanovolt per meter per square root Hz when measured at 1 Hz;
c. "Magnetic gradiometers" as follows:
1. "Magnetic gradiometers" using multiple "magnetometers" specified in 6.A.6.a.;
2. Fibre optic "intrinsic magnetic gradiometers" having a magnetic gradient field 'sensitivity' less (better) than 0.3 nT/m (rms) per square root Hz;
3. "Intrinsic magnetic gradiometers", using "technology" other than fibre-optic "technology", having a magnetic gradient field 'sensitivity' less (better) than 0.015 nT/m (rms) per square root Hz;
d. "Compensation systems" for magnetic or underwater electric field sensors resulting in a performance equal to or better than the parameters specified in 6.A.6.a., 6.A.6.b., or 6.A.6.c.;
e. Underwater electromagnetic receivers incorporating magnetic field sensors specified in 6.A.6.a. or underwater electric field sensors specified in 6.A.6.b.
Technical Note
For the purposes of 6.A.6., 'sensitivity' (noise level) is the root mean square of the device-limited noise floor which is the lowest signal that can be measured.
GRAVIMETERS