Rounding Policy
Purpose
This page specifies the rounding conventions applied to all calculator results. Every calculator links to this policy to ensure users understand the precision of displayed results.
Displayed Precision
Chemical concentrations (ppm): displayed to 1 decimal place. pH: displayed to 2 decimal places. LSI: displayed to 2 decimal places. Temperatures (°F, °C): displayed to 1 decimal place. Volume (gallons, liters): displayed as whole numbers. Dosage (fl oz, oz, lbs): displayed to 1 decimal place for quantities under 10, whole numbers for 10 and above.
Internal Precision
All intermediate calculations are performed in full JavaScript floating-point precision (IEEE 754 double, approximately 15–17 significant digits). Rounding is applied only at the final display step, not at intermediate calculation steps. This prevents compounding rounding errors in multi-step calculations.
Unit Conversions
Unit conversions use the exact factors defined in data/datasets/conversion-factors.json. For example, gallons to liters uses exactly 3.785411784 (the NIST definition). No rounded approximations are used in intermediate calculations.
Rounding Order
(1) Perform all calculations in full floating-point precision; (2) Apply unit conversion if required; (3) Round only the final displayed value to the specified decimal places. Intermediate values passed between calculation steps are not rounded.
Examples
FC change needed: calculated as 2.00 ppm → displayed as "2.0 ppm". Muriatic acid dose: calculated as 9.876 fl oz → displayed as "9.9 fl oz". Pool volume: 24,831.4 gallons → displayed as "24,831 gallons". LSI: −0.1234 → displayed as "−0.12". Note: displayed rounding does not affect calculation accuracy — all intermediate values retain full precision.
Relationship to Confidence
The precision of displayed results does not imply that accuracy is equivalent to the displayed decimal places. A result of "9.9 fl oz" is precise to 0.1 fl oz but may have an accuracy uncertainty of ±10–15% due to product concentration variation, pool volume estimation, and measurement error. See the Precision Policy for full uncertainty discussion.