Health guides
One formula per guide, taken apart term by term, with the error its own source reports and the calculator that runs it. Every figure is traceable to a published document.
How TDEE is calculated, in full
The complete derivation of total daily energy expenditure: the Mifflin-St Jeor equation term by term, the two equations that compete with it, the activity ladder that has no primary source, the published activity bands that do, and the error band that belongs around the result.
Read the guide →Reading an A1C result
What the A1C measurement is, the two unit systems it is reported in, the equation that translates it into an average glucose, the tolerance the assay itself carries, the ranges the ADA defines, and the several things a single A1C value cannot tell you.
Read the guide →What heart rate zones actually mean
Heart rate zones are percentages of an estimated ceiling, drawn at edges nobody published. This guide separates the five-zone convention from ACSM's published intensity classification, sets Karvonen against percent-of-maximum, and quantifies how much each choice moves the boundaries.
Read the guide →How pregnancy dating works
Why a due date is counted from the last period rather than conception, what the 280-day convention assumes, how cycle length shifts it, why a first-trimester scan supersedes the arithmetic, and why term is a five-week window rather than a date.
Read the guide →