Version 1.1 methodology
Method and sources
Colonygrid keeps calculation rules, review boundaries, capture caveats, and primary references visible beside the work. The governing laboratory method and SOP remain authoritative.
Research-use boundary
Colonygrid supports research, educational, environmental, and food-laboratory plate documentation. It does not identify organisms, diagnose conditions, validate a method, certify compliance, or replace a laboratory's SOP, quality system, analyst judgment, or release authority.
Capture diagnostics
The tonal-range, clipping, edge-detail, illumination, and plate-ROI checks are deterministic image diagnostics intended to help an analyst notice capture problems. They do not establish analytical validity, organism identity, incubation adequacy, media suitability, or compliance with a laboratory method.
Count review ranges
The FDA BAM 2026 preset uses the 15-to-300 colony range described in the January 2026 aerobic plate count chapter. The USDA/AOAC 30-to-300 convention remains a separate selectable policy. Custom bounds are labeled with the user's SOP identifier. Colonygrid does not convert one convention into another.
Weighted APC record
APC = total exact colonies / total original-homogenate volume received by contributing plates
Original-homogenate volume equals plated volume multiplied by the dilution ratio. This weights plates by the amount of original sample they received rather than averaging per-plate concentrations equally. Colonygrid rounds only the final report value to two significant digits using half-even handling.
No growth, TNTC, and excluded observations
When all included dilutions show no colonies, Colonygrid reports a less-than boundary based on the lowest included dilution instead of inventing zero. A TNTC observation blocks the app's simple weighted arithmetic and directs the analyst to maximum-likelihood handling. Spreader and laboratory-accident dispositions remain visible in the evidence record but are excluded from that arithmetic.
Review and evidence integrity
A reviewer signature records the exact analysis revision, automatic count, final count, additions, exclusions, disposition, dilution exponent, and plated volume reviewed. Changing a governed input makes the review stale. Each evidence package is marked READY or DRAFT and inventories every payload with SHA-256 and byte count. These controls preserve provenance; they do not provide electronic-signature certification or regulatory compliance by themselves.
Primary references
- U.S. FDA Bacteriological Analytical Manual, Chapter 3: Aerobic Plate CountJanuary 2026 chapter used for the FDA preset, report rounding examples, and APC workflow context.
- U.S. FDA Aerobic Plate Count CalculatorOfficial calculator offered when an observation requires maximum-likelihood handling.
- ISO/TC 34/SC 9: ISO 7218 general requirements and guidanceGeneral microbiology framework reference. Colonygrid does not claim ISO conformity or method validation.
Version note
This page describes Colonygrid 1.1 and was last reviewed on August 27, 2026. A laboratory's current validated method, SOP, and quality system take precedence over app defaults.