Some particularly thorough research was done in the early 1960’s by Cutkosky and Lee. They constructed two versions of fused-silica based capacitors and characterized most of the important features of these standards.
The set of twelve that they created contained several standards which were exceptionally stable.
These and several later ones have been used ever since as the primary capacitance standards of the United States.
Andeen Hagerling's primary standards are calibrated on a regular basis against the calculable capacitor at NIST.
The latter is now the ultimate reference.
Andeen Hagerling capacitance standards
- AH 2700A – Ultra-precision capacitance bridge, 50Hz - 20kHz
- AH 1100 – The World’s most stable capacitance standard
- AH 11A standard
- AH 2550A – 1kHz automatic capacitance bridge
- AH 2500A – 1kHz automatic capacitance bridge
- DCOAX Cable – Dual, low noise, coaxial cable optimized for three-terminal capacitance measurements
- AHTTA1 – Test adapter for ARCO SS-32 and GR1409 standard capacitors