Description
Divide sample pressure by reference pressure.
A food measurement can require calibration, recovery correction or a defined reference state. A corrected value or reporting envelope is only one analytical step and does not independently establish contamination status, shelf life or safety.
Divide sample pressure by reference pressure.
When to use this tool
Use Food Water Activity Reference Ratio Term when you need the specified laboratory or bench-measurement term.
How to use the tool and how it works
- Enter sampleVaporPressure, referenceVaporPressure, sameTemperature. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read activityRatio. Use the output convention below.
Require positive reference vapor pressure, sample pressure from zero through reference, and sameTemperature true. Divide sample pressure by reference pressure.1
Water activity uses equilibrium sample/pure-water vapor pressures at the same temperature. It is distinct from moisture content; the ratio alone is not a safety verdict.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| sampleVaporPressure | Sample Vapor Pressure | Required. Finite number; minimum 0. |
| referenceVaporPressure | Positive pure-water equilibrium vapor pressure at the sample temperature for water-activity interpretation. | Required. Finite number; strictly above 0. |
| sameTemperature | Required true assertion; temperature equality is not measured. | Required. Boolean. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| activityRatio | Activity Ratio Unit: 1. | Required. Finite number. |
{
"input": {
"sampleVaporPressure": 2,
"referenceVaporPressure": 4,
"sameTemperature": true
},
"output": {
"activityRatio": 0.5
}
}Limitations and assumptions
- Reference is pure-water equilibrium vapor pressure at the same temperature for a water-activity interpretation. The ratio alone does not establish safe food, shelf life, or microbial growth limits.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use a validated analytical method and the appropriate safety assessment. Review reference conditions, units, uncertainty, recovery and product-specific interpretation rather than inferring safety from a single number.
References
-
Calculation and input contract: food-safety/food-water-activity-reference-ratio-term — tool.io
-
Water activity in food — CSIRO, hosted by USDA Agricultural Research Service
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