There is lot more work under the hood.
Part: 1 the XFR 4 parameters represents the 23 order 2 segments poly from CIPM.
No comment !
Parts: 2, 3, 4 explore these 3 ranges based on the inverse models.
An example to calibrate the XTR is given.
Roughly, a good installation from reputed suppliers should render ± 0.01 °C.
Any question, please don't hesitate.

Cheers ... Jean

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