PS - I just did some tests on the Duet WiFi on my bench:
1K resistor reads -2.7C to -3.0C. It should be 0.0C, so if my resistors are accurate then it is under-reading by almost 3C.
2K resistor reads 266.9 to 267.6C. It should be 266.3C, so if my resistor is accurate then it is over-reading by about 0.5C.
These are with zero L and H correction. I then tried the same resistors on a Duet Maestro:
1K gave -0.8 to -1.0C (under reading by 0.9C)
2K gave 270.3 to 270.7C (over reading by 4.2C)
The Maestro can measure PT1000 sensors more accurately. I think I may be able to improve on the error at low temperatures on the Duet WiFi.