Calibration and Residuals — Instrument Linearity
A calibration series against the ideal one-to-one line, with the residuals plotted on the same axes so the departure is visible rather than inferred. Shows a reference line drawn from a formula, which is the honest way to put a comparison on a figure — the line is a stated relationship, not a fit to the points beside it.
Make it your own.
title: Instrument calibration against certified standards
subtitle: Six certified reference materials, triplicate reads
x: Certified value (mg/kg)
y: Measured value (mg/kg)
grid: both
legend: right
scatter "Measured" error: sd
10, 10.4 ± 0.3
25, 25.9 ± 0.5
50, 51.2 ± 0.8
100, 102.6 ± 1.4
200, 205.1 ± 2.6
400, 411.8 ± 5.2
plot "Ideal (y = x)" y = x for x in [0, 420] dashed: yes
note: The dashed line is y = x, the relationship the instrument is supposed to have. It is drawn from that formula, not fitted to the points — a fitted line through these points would pass close to them by construction and would show nothing.