Table 2.

Comparison of observed values of temperature of some defining fixed points and secondary reference points on the various provisional temperature scales adjusted to the IPTS–68

Equilibrium point and assigned temperature on the IPTS–68	Temperature scalea	Temperature value	Year of work	Reference
e–H2, TP	NBSb	13.799	1951	[13]
13.81 K	NPL	13.813	1963	[14]
	NBS	13.8051	1971	[15]
	NBS	13.8079	1971	[16]
e–H2, BP	NBS	17.04261	1971	[15]
(25/76 atm)
17.042 K
e–H2, NBP	NBSb	20.276	1951	[13]
20.28 K	NBS	20.276	1962	[17]
	NPL	20.2796	1963	[14]
	NBS	20.27819	1971	[15]
	NBS	20.2798	1971	[16]
Ne, NBP	NBS	27.099	1962	[18]
27.102 K	NBS	27.103	1970	[19]
	NBS	27.1032	1970	[20]
	NBS	27.103	1972	[32]
O2, TP	NBS	54.3576	1966	[21]
54.361 K
O2, NBP	NBS	90.1956	1966	[21]
90.188 K	NBS	90.1912	1966	[21]
	NBS	90.1924	1966	[21]
	PSU	90.1928	1966	[21]
	PSU	90.1919	1966	[21]
	NPL	90.1900	1966	[21]
	NPL	90.1935	1966	[21]
	PRMI	90.1935	1966	[21]
	PRMI	90.1937	1966	[21]
	PRMI	90.1948	1966	[21]
Ne, TP	NBS	24.552	1962	[18]
24.555 K	NBS	24.561	1970	[19]
	NBS	24.560	1970	[20]
	IPTS–68c	24.5620	1971	[22]
	IPTS–68c	24.5618	1971	[22]
N2, TP	NBS	63.1481	1966	[23]
63.148 K	NBS	63.1469	1966	[23]
	PRMI	63.1479	1966	[23]
	PRMI	63.1477	1966	[23]
N2,NBP	NBSb	77.3459	1954	[24]
77.348 K	NBS	77.3466	1963	[25]
	NBS (1)d	77.3493	1966	[26]
	NBS (1)d	77.3471	1966	[26]
	NBS (2)d	77.3481	1966	[26]
	PRMI	77.3475	1966	[26]
	PRMI	77.3477	1966	[26]
	NPL (3)d	77.3469	1966	[26]
	NPL (3)d	77.3473	1966	[26]
	NPL (4)d	77.3486	1966	[26]

^aNBS = NBS–IPTS–68, NPL = NPL–IPTS–68, PRMI = PRMI–IPTS–68, and PSU = PSU–IPTS–68.

^bInitially published on the NBS–1939 scale.

^cThe prt was calibrated at the IPTS–68 defining fixed-points.

^dThe number identifies the prt.