Natural unit of action in eV s
UnitsExact
= 6.582 119 569… × 10−16 eV s
- Value
- 6.582 119 569… × 10−16 eV s
- Standard uncertainty
- exact
- Relative uncertainty
- exact
- Status
- Exact since the 2019 SI redefinition
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
NIST prints this exact value cut to 10 digits. ConstantID recomputes it from the defining constants: 6.582 119 569 509 065 698 073 512 182 44 × 10−16…
Use in a calculation
# natural unit of action in eV s, CODATA 2022 (NIST)
natural_unit_of_action_in_ev_s = 6.5821195695090656980735121824419313e-16 # eV s, exact
# SciPy: scipy.constants.physical_constants['natural unit of action in eV s']What it is
The unit of action in the natural units of relativistic quantum mechanics, where ħ, c and the electron mass are set to 1.
It is built only from constants that have exact values since 20 May 2019, so it is exact too; CODATA 2018 was the first adjustment to list it that way.
In other units
| Unit | Value | |
|---|---|---|
| CGS (cm2 g s−1) | 1.054 571 818 × 10−27 | exact |
Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display.
How the value changed, 1998–2022
Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart). Diamonds mark adjustments in which the value was exact.
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | 6.582 119 569… × 10−16 | exact | exact |
| 2018 | 6.582 119 569… × 10−16 | exact | +1.4 σ of 2014 |
| 2014 | 6.582 119 514(40) × 10−16 | 6.1 × 10−9 | +1.6 σ of 2010 |
| 2010 | 6.582 119 28(15) × 10−16 | 2.3 × 10−8 | +1.8 σ of 2006 |
| 2006 | 6.582 118 99(16) × 10−16 | 2.4 × 10−8 | −0.3 σ of 2002 |
| 2002 | 6.582 119 15(56) × 10−16 | 8.5 × 10−8 | +1.0 σ of 1998 |
| 1998 | 6.582 118 89(26) × 10−16 | 4.0 × 10−8 |
“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).