Also worth reading is,

Euromet Guides - No. 13 | Guidelines on the Calibration of Temperature Block Calibrators | TC-T | Version 4.0, 09/2017

https://www.euramet.org/publications-media-centre/calibration-guidelines

While it is easy to do the maths to go from Temp to Ohms, doing the ohm to temp is another issue. I like maths but I don't know it well enough to work out the best way to do it, and of course any documentation I find is always assuming I understand coding and maths to a level beyond my comprehension.

A recommended way to do this is given in Nicholas & White on page 242. They use a recursive technique: an initial approximate solution is improved by repeated application of a 'polishing' function.

Given a measured resistance ratio W(t), i.e. the ratio of the measured resistance to the resistance at 0˚C (nominally 100Ω, but you can use a measured calibration value) and the PRT100 formula constants A, B, and C, calculate an initial temperature estimate t0 (in ˚C) using the quadratic formula on the equation:

W(t) = 1 + A*t0 + B* t0^2

Then use the calculated t0 to calculate t1:

t1 = (W(t) - 1)/(A + B*t0 + C*t0^2*(t0 - 100))

(the C term is only required if t0 > 0 ˚C)

For 'normal' temperatures, one application of the iteration is 'good enough', but you can repeat it to claculate t2 in terms of 1, etc.

This is simple enough to set up in Excel: then you can play with it and compare the results with published PRT tables, to convince yourself it works!