Two spectrophotometers can give different readings without either one being “wrong.” Work from the sample and measurement method outward before changing an instrument or applying an arbitrary offset.
Use this diagnostic order
- Identify what differs. Is it L*a*b*, the spectrum, ΔE, pass/fail status or only rounded reporting?
- Confirm sample and reference. Use the same stable, representative sample, location, backing and orientation.
- Align calculations. Match illuminant, observer, color space, ΔE formula and any formula parameters. Changing ΔE formula changes the difference result, not the underlying Lab coordinates.
- Align optics and handling. Match geometry, SCI/SCE, aperture, UV/excitation condition, positioning and measurement count.
- Check each instrument independently. Follow its approved routine, inspect standards and ports, then verify with the same approved check sample.
- Compare representative materials. Use a panel of relevant colors, finishes and textures—not one white tile alone.
When to escalate
Record instrument IDs, firmware/software versions, method settings, reference IDs, individual readings, spectra where available and the sample condition. Contamination, drift, wavelength range or bandwidth differences, reporting precision and material fluorescence can all matter. If an approved method remains misaligned after the checks, involve the instrument supplier or metrology lead rather than forcing a correction.
Also read repeatability vs inter-instrument agreement and standardisation and calibration.
Last reviewed 21/09/2026 · Level: Fundamental
Topics
Applications
Related knowledge
Inter-Instrument Agreement
Spectrophotometer Repeatability vs Inter-Instrument Agreement
Repeatability shows how closely one spectrophotometer agrees with itself. Inter-instrument agreement shows how closely it agrees with another. Learn why both matter for reliable color control.
7–9 minute guide · Read the guide →Measurement Techniques
How to Measure Color Correctly: A Practical Guide
Learn how to measure color correctly: control calibration, settings, sample presentation, orientation and averaging so every spectrophotometer result is repeatable and useful.
8–10 minute guide · Read the guide →Aperture Size
Measurement Aperture Size Explained: Why It Matters
Aperture, illumination area and detector view are not always the same. Match the instrument’s usable measurement area to the sample and method.
Quick technical guide · Read the guide →Calibration & Maintenance
How to Calibrate a Spectrophotometer
Routine standardisation, verification and formal calibration are distinct activities. Follow the instrument manual and record every approved check.
Quick technical guide · Read the guide →CIELAB
CIE L*a*b* Explained: Understanding L*, a* and b*
CIE L*a*b* describes color with three coordinates: L* lightness, a* red–green and b* yellow–blue. Learn how to interpret Lab values for practical quality control.
4–5 minute guide · Read the guide →Delta E
Measuring Tile Color
Measure tile color with controlled firing state, face, pattern, gloss, orientation, aperture and batch sampling, while applying ISO 10545-16 only within its scope.
Technical guide · Read the guide →