Table 2.

Standard uncertainties u_s×10⁶ from various sources in the re-determination of (T−T₉₀)/T. The square root of the sum of the squares (RSS) is calculated twice: first, including Rows 4 and 5, but not Rows 6 and 7; and second, including Rows 6 and 7, but not Rows 4 and 5

Source	217 K	234 K	253 K	293 K	303 K
Microwave values for [a(T)/a(Tw)]2
1. Discrepancies among triplets	0.32	0.27	0.25	0.27	0.33
2. δm(T) calc. from resistivity (0.04×ρ)	0.39	0.25	0.12	0.12	0.18
3. δm(T) calc.−δm(T) meas.	0.24	0.24	0.24	0.24	0.24
Acoustic (isotherm fits)
4. Uncertainty of A0(Tw)/a2	1.67	1.67	1.67	1.67	1.67
5. Uncertainty of A0(T)/a2	2.31	1.85	1.35	1.67	1.43
Acoustic (surface fit)
6. Uncertainty of A0(Tw)/a2	0.25	0.25	0.25	0.25	0.25
7. Uncertainty of A0(T)/a2	0.52	0.38	0.36	0.31	0.38
Thermometry
8. SPRT & bridge repeat. @ Tw (10 μΩ)	0.46	0.43	0.40	0.34	0.33
9. Difference between calibrations	0.22	0.15	0.10	0.54	0.78
10. Temperature gradient	0.46	0.43	0.40	0.34	0.33
11. Non-uniqueness of ITS-90	0.9	0.0	0.8	0.6	0.0
Additional sources
12. Thermal conductivity (0.3 %)	0.20	0.20	0.20	0.20	0.20
13. Uncertainty of pressure zero	0.21	0.12	0.05	0.03	0.07
14. Isotherm fits: RSS	3.13	2.62	2.40	2.58	2.43
15. Surface fit: RSS	1.42	0.92	1.16	1.11	1.13
16. Isotherm fits: RSS×(T/mK)	0.68	0.61	0.61	0.76	0.74
17. Surface fit: RSS×(T/mK)	0.31	0.22	0.29	0.33	0.34