ADH minimum-PMI Calculator

Run the ADH mPMI Calculator Fullscreen

About This MicroSim

Blowfly larvae develop at a rate that depends on temperature. Forensic entomologists exploit this by counting Accumulated Degree Hours (ADH) — the sum, over time, of the temperature above a species-specific base temperature. Each developmental stage requires a known number of degree-hours to reach. By counting degree-hours backward from when a body is discovered until the total reaches the threshold for the observed stage, an analyst estimates the minimum post-mortem interval (mPMI) — the earliest the death could have occurred.

This MicroSim lets you perform that calculation. Set a 7-day mean-temperature record, pick a species and larval stage, and watch the cumulative ADH accumulate back from the discovery day until it crosses the published threshold.

How to Use It

1. Choose an insect species and the developmental stage observed on the body. The stage sets the ADH threshold.
2. Adjust the Base Temp slider (the temperature below which development stops — it defaults to the species value).
3. Click any temperature bar to select that day, then use the Day Temp slider to edit its mean temperature.
4. Press Calculate mPMI. The orange curve accumulates degree-hours back from discovery; the green marker shows where it meets the red threshold line.
5. Read the minimum PMI (in days) in the green result panel.

What You Can Learn

• Calculate accumulated degree-hours from a temperature record and base temperature.
• Explain why warmer weather shortens the estimated PMI and cooler weather lengthens it.
• Interpret the crossing of cumulative ADH with a stage threshold as the earliest possible time of death.

You can embed this MicroSim on your own web page with this iframe:

<iframe src="https://dmccreary.github.io/forensic-science/sims/adh-mpmi-calculator/main.html"
        width="100%" height="547" scrolling="no"></iframe>

Lesson Plan

Audience: High-school forensic science (grades 9–12) Time: 15–20 minutes Bloom level: Apply (L3) — calculate minimum PMI.

Worked calculation. Walk students through one full calculation by hand for a single day (ADH = (meanTemp − base) × 24), then let them verify the running total against the simulator's cumulative curve.

Guided questions:

• Raise every day's temperature by 5°C. Does the estimated mPMI get longer or shorter? Why?
• Switch the species from Calliphora vicina (base 2°C) to Lucilia sericata (base 9°C) at the same temperatures. What happens to the accumulated ADH, and why?
• Why is this called the minimum PMI rather than the exact time of death?

Extension. Have students research real published ADH thresholds and discuss how measurement error in the temperature record propagates into the mPMI estimate.

References

• Forensic entomology (Wikipedia) — using insects to estimate time of death.
• Growing degree-day (Wikipedia) — the accumulated-temperature method adapted here as degree-hours.
• Post-mortem interval (Wikipedia) — what the calculation estimates.
• p5.js reference — the library used to build this simulation.

Specification

This MicroSim was generated from a specification in Chapter 12: Forensic Entomology and Decomposition Analysis.

Design note: the specification calls for an editable hourly table across 7 days (168 values). To keep the interface usable in a small embedded canvas, the model uses 7 editable daily mean temperatures (ADH = (mean − base) × 24 per day). The ADH thresholds are illustrative reference values for teaching the method, not casework figures.