Precision Policy
Purpose
This page describes how WaterBalanceTools handles floating-point arithmetic, measurement uncertainty, and the relationship between calculated precision and real-world accuracy.
Floating-Point Handling
All calculations use standard IEEE 754 double-precision floating-point arithmetic as provided by the JavaScript runtime. This provides approximately 15–17 significant digits of precision. Known floating-point edge cases (e.g., 0.1 + 0.2 ≠ 0.3 exactly) do not affect pool chemistry calculations at the precision levels required.
Displayed Decimals
See the Rounding Policy for specific decimal place rules. Displayed precision is chosen to reflect meaningful measurement resolution — for example, showing pH to 2 decimal places matches the resolution of digital pH meters and high-quality DPD test kits.
Measurement Uncertainty
Pool water test results have inherent uncertainty based on the test method used. Test strips: ±0.5 ppm FC, ±0.5 pH. Liquid DPD drop test (Taylor K-2006): ±0.2 ppm FC, ±0.2 pH. Digital photometer: ±0.05 ppm FC, ±0.05 pH. Calculator inputs are only as accurate as the test used to produce them.
Recommended Retesting After Chemical Additions
After adding chemicals: wait at least 30 minutes with pump running before retesting pH or alkalinity; wait 4–8 hours (or overnight) for full equilibration of pH, alkalinity, and calcium adjustments; wait 24 hours for CYA additions (CYA dissolves slowly); retest chlorine as needed based on current demand.
Relationship to Confidence Ratings
Confidence ratings reflect the strength of the underlying scientific or industry evidence for a value or recommendation. They do not directly reflect the mathematical precision of the calculation. A Very High confidence rating means the formula or value is strongly supported by evidence — it does not mean the calculated result will be precise to the displayed decimal place in real-world conditions.