Use this plant measurement when samples, dry- or fresh-mass basis, image threshold, geometry, instrument calibration, and treatment timing follow one consistent protocol.

Conversion factor

Documented linear approximation factor mapping SPAD units to micrograms per square centimeter; defaults to 0.4 and must lie between 0 and 2.

SPAD value

SPAD meter reading; must not be negative.

The implementation follows this calculation rule: Estimate chlorophyll content from a SPAD reading with the documented linear approximation chlorophyll = SPAD value times conversion factor, where the factor defaults to 0.4.

Chlorophyll estimate

Estimated chlorophyll content in micrograms per square centimeter.

Pigment proxies, canopy metrics, tissue density, and leakage indices are method-dependent. Species, developmental stage, hydration, illumination, extraction efficiency, sensor angle, and environmental conditions can confound comparisons. The output is explicitly an estimate or proxy; preserve that label when reporting it.

Pair the proxy with calibrated chemical analysis, destructive biomass sampling, or repeated field measurements where practical. Report environmental conditions and whether values use fresh mass, dry mass, area, or volume.

• Chl a/b Ratio

  Compute the chlorophyll a to chlorophyll b ratio from pigment concentrations in micrograms per milliliter.

• Carotenoid Content

  Estimate total carotenoid content in micrograms per gram of leaf fresh mass as the absorbance at 480 nanometers times four divided by the fresh mass, following the documented Arnon-proxy extinction scaling.

• Anthocyanin Content

  Compute anthocyanin content in micrograms per gram of dry mass as the corrected absorbance divided by the dry mass times an extinction scale factor that defaults to one hundred; apply any baseline correction to the absorbance upstream before passing it in.