Cross-subject methods
Know which rule the calculator is using
The same word—“uncertainty”—can refer to different ideas. These tools keep school-lab propagation rules separate from SD, SE, confidence intervals and formal statistical models.
Uncertainty propagation used in the toolkit
| Operation | Physics | Chemistry | Biology |
|---|---|---|---|
| Add / subtract | Add absolute uncertainties when using the school-lab worst-case rule. | Add absolute uncertainties for the school-lab rule used by the calculator. | Use only when the biological calculation is being treated as a measurement-propagation problem; do not substitute this for SD/SE. |
| Multiply / divide | Add fractional or percentage uncertainties as a first-order school-lab approximation. | Add percentage uncertainties in the toolkit’s course-level calculator. | When appropriate to a measurement calculation, use the stated propagation convention; biological variation still needs its own statistical treatment. |
| Power xⁿ | Multiply fractional uncertainty by |n| as a first-order estimate. | The toolkit marks power propagation as HL-only; follow the current course/teacher convention for your task. | Not treated as a general substitute for statistical uncertainty; use only when the task explicitly calls for measurement propagation. |
These linear school-lab rules are not the same as combining independent standard uncertainties in quadrature. Each subject About page explains its own assumptions in more detail.
Reporting and rounding
- Keep extra digits in intermediate calculations.
- Report a final uncertainty to one or two significant figures unless your task specifies otherwise.
- Round the measured value to the same decimal place as its final absolute uncertainty.
- Chemistry tools distinguish an unrounded calculated value from a suggested report value where appropriate.
- Units and model assumptions matter as much as the arithmetic.
Regression and graphs
Ordinary least squares, r and R² describe the selected numerical model; they do not prove causation, physical validity or absence of systematic error. Error bars must be identified as uncertainty, SD, SE or another quantity before interpretation.
Subject method pages
Physics calculation methods · Chemistry calculation methods · Biology statistics and methods