Methodology
IfSketch is a collection of transparent models, not a black box. This page is the house style for how those models are built, labelled and checked.
How calculations work
Each experiment has a pure function: given the current inputs, it returns a result. There is no hidden server step and no language model in the loop. If you refresh the page with the same query string, you get the same number. Floating-point values are rounded for display so you never see £18,249.999999.
How assumptions are selected
Defaults are round, UK-flavoured where money is involved, and conservative where a rate would otherwise look like a promise. Savings pages default growth to a modest figure or to zero. Science pages use conventional constants (standard gravity, IAU astronomical unit, sea-level speed of sound) and say when a scenario is a thought experiment rather than known physics.
Why results are estimates
A lifetime of sleep is not eight hours times every night you have lived. A standing order is not a fee-free, tax-free, inflation-free annuity. Planetary “what ifs” freeze most of the universe so one variable can move. The useful output is the direction and the order of magnitude, plus a sentence that says what was left out.
How scientific scenarios are simplified
When a full simulation is impossible or dishonest, the page uses a textbook model and names it: uniform-density gravity trains, Wien's law for a black body, ρgh for water pressure. Impossible requests (stop time, breathe with fictional gills) are labelled as stories with physics-shaped edges, not as predictions.
How sources are selected
Prefer primary references: national metrology (NIST, BIPM), space agencies' fact sheets (NASA), statistical agencies (ONS), and official UK guidance (gov.uk, NHS, MoneyHelper, Bank of England) for context. Sources are not invented, and a constant's source is listed next to the experiment that uses it.
How calculations are checked
Shared helpers for time, money and physics have unit tests for the ugly cases: NaN inputs, zero rates, jump recoil that must stay tiny, a gravity-train time near 42 minutes. Display helpers round currency to whole pounds unless pence are requested. If an input is out of range it is clamped; if a result is not finite it is not shown as a fake number.