Linear regression lines for each year of data analysis for international normalized ratio (INR) testing by New South Wales (NSW) Health Pathology (Pathology West, West, or Rural/Regional) network laboratory participants (27 laboratories; 35 regression lines in each case) of the Royal College of Pathologists of Australasia Quality Assurance Program: (A) 2017 Stago, (B) 2018 Stago, (C) 2019 Stago, (D) 2021 Werfen, (E) 2022 Werfen, and (F) 2023 Werfen. NSW Health Pathology network laboratory participants used Stago instruments (STA-R Evolution, STA-Compact Max, or STA-Satellite) and Neoplastine CI Plus then NeoPTimal PT reagent in 2017 to 2019 inclusive, as well as Werfen instruments (ACL TOP family [350, 550, or 750]) and HemosIL RecombiPlasTin 2G PT reagent in 2021 to 2023 inclusive. The line of identity (or equivalence) is shown in each figure as the black line from bottom left to top right of each figure. Westmead-based Institute of Clinical Pathology and Medical Research laboratory data (2 instruments, so 2 lines) shown as solid red lines in each figure. Occasional data (blue circles) reflect random errors (1 example in 2017, 3 examples in 2019) or transcription errors (reversal of data entry; 4 examples in 2021). The effect of a large random error on the regression line is highlighted with a blue arrow in C (2019).