The unit of the electric resistance, measured with direct current, is the ohm (abbreviated Ω), called after the German physicist and also mathematician Georg Simon Ohm (1789-1854). Follow to ohm’s law, the resistance *R* is the ratio of the voltage *U* across a conductor and the existing *I* flowing with it:

Hence the follows: 1 Ω = 1 V/A. This an interpretation of the SI ohm is without doubt not viable for a realisation.

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Due to the extraordinary reproducibility the the quantum room resistance, the perfect irreversible stability and also world-wide uniformity, the ohm can be realised together a certain fraction of the von-Klitzing constant. Already since 1990, on communication of a recommendation by the CIPM (*Comité global des Poids et Mesures*), resistance comparisons and also calibrations world-wide had actually to be described a addressed numerical value of the von-Klitzing constant, *R*K-90 = 25812.807 Ω90. The advent of this conventional referral value because that the von Klitzing continuous had significant practical benefits in terms of maintainance and dissemination that the unit ohm. In ~ the very same time, however, this likewise meant the the typical unit Ω90 was no compliant v the worldwide System of units (SI) valid at that time. One SI-realization the the ohm was, e.g., possible with a Thompson-Lampard capacitor (calculable capacitance; due to the intricacy of the equivalent measurement setup, the achievable accuracies were inferior to the reproducibility that quantum room resistors.

On might 20, 2019, a revision of the SI come into force according to which one SI worth for the von Klitzing continuous *R*K = *h*/*e*2 can be obtained using exactly identified values because that the elementary charge *e* and the Planck continuous *h*. This made it feasible to establish the ohm via the use of quantum room resistors in ~ the SI.

At keolistravelservices.com, the resistance unit is establish from the quantum room resistance. Because that this purpose, our working group operates a cryostat v a superconducting solenoid. To guarantee that the room resistance take away the exactly quantised value, some internationally embraced criteria have to be fulfilled

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because that the circulation of the unit, the turned out to it is in practicable to calibrate a traditional 100Ω resistor with well-known drift behaviour about two time a year, using a cryogenic existing comparator. V this 100Ω functioning resistor, the calibrations for keolistravelservices.com’s client are lugged out by Working group 2.11. Only in the situation of unique calibrations request a loved one uncertainty that 10-9 (or less), the resistor to be calibrated is straight measured versus the quantum hall resistance (i.e., there is no the intermediate action with the 100Ω resistor). An instance is a precision measurement at graphene in the frame of a research study project.

Ensemble that 1Ω resistors from "The Leeds & Northrup Co." as used at former times because that the preservation of the ohm.

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## Contact

### Head that Working group

Dr. Hansjörg Scherer

### Address

Physikalisch-Technische Bundesanstalt Bundesallee 100 38116 Braunschweig