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.
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How calculations work
Each experiment is a fixed formula: given the current inputs, it returns a result, worked out in your browser. If you reload the page with the same settings, you get the same number. Results are rounded for display, so you see £18,250 rather than £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 would be misleading, 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 clearly labelled as stories that borrow real physics, 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. Each constant's source is listed on the experiment that uses it, and every source appears on the Sources page.
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.