Useful numbers need visible assumptions.
Every tannerd.net calculator is built around a narrow question, a visible formula, editable assumptions, and a result that explains what the number means.
1. Separate arithmetic from assumptions
Basic arithmetic is deterministic. Product coverage, fee rates, waste factors, overtime thresholds, return rates and similar assumptions can vary. When a number can vary, the calculator should either make it editable or identify the source and review date.
2. Prefer decision outputs
A calculator should not stop at one number when the useful decision requires context. Seller tools show profit, ROI and margin. Driving tools distinguish fuel cost from total cost per mile. Contractor tools separate markup from margin.
3. Avoid pretending estimates are facts
Planning calculators do not replace an invoice, payroll system, tax return, engineering takeoff, code review or professional judgment. Results are labeled as estimates where the inputs themselves are estimates.
4. Protect calculator inputs
Calculator values are processed in the browser. Some tools save entered values to browser local storage for convenience; those calculator values are not intentionally sent to tannerd.net.
5. Review meaningful formula changes
Tools with externally sourced assumptions include source links and review dates where practical. General arithmetic calculators use formulas shown directly on the page so users can check the work.
Citation and AI search
The site is designed so important formulas, assumptions, examples, and source links are present in static HTML and can be understood without running the calculator. AI search and grounding systems are explicitly allowed to crawl and reference public pages. Model-training permission is treated separately from search and real-time grounding access.
The formula reference consolidates commonly useful equations without creating separate thin pages for every wording of the same question.
Corrections
If a formula, assumption or explanation appears wrong, use the contact page and include the calculator name and the inputs that produced the issue.
Public calculator API
Selected deterministic calculators are also exposed through a read-only JSON API. API outputs use the same formulas as the corresponding browser tools and include a source URL back to the human-facing explanation. See API documentation.