Conventional value of ohm-90

$Ω_{90}$ = 1.000 000 017 79… Ω

Value: 1.000 000 017 79… Ω
Standard uncertainty: exact
Relative uncertainty: exact
Status: Exact
Symbol: $Ω_{90}$
Source: CODATA 2022 via NIST · NIST entry

NIST prints this exact value cut to 12 digits. ConstantID recomputes it from the defining constants: 1.000 000 017 793 667 564 323 613 3407…

Use in a calculation

# conventional value of ohm-90, CODATA 2022 (NIST)
conventional_value_of_ohm_90 = 1.0000000177936675643236133406989578  # ohm, exact

# SciPy: scipy.constants.physical_constants['conventional value of ohm-90']

What it is

The size of the practical ohm used in electrical metrology from 1990 to 2019 (based on K_J-90 and R_K-90), in SI ohms. It is exact because the elementary charge and Planck constant are now exact.

It is built only from constants with exact values, so it is exact too.

How the value changed, 1998–2022

CODATA	Value (uncertainty)	Relative uncertainty	Change from previous
2022	1.000 000 017 79…	exact	exact
2018	1.000 000 017 79…	exact

“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).