The foundations underneath the rest of the site — trigonometry, a full geometry suite for 2D and 3D shapes, statistics & probability, a graphing calculator for plotting any function by hand, and ISO week numbers for the calendar arithmetic everyone gets wrong.
How long until any date in every unit at once — and how many working days that really is, with Easter and the weekend substitution rules computed rather than looked up.
The ISO week for any date and the dates any week covers — plus which years have 53 weeks, and where the US Sunday-start convention gives a different answer.
The angle between the hour and minute hands at any time, with the working shown — plus every moment the hands overlap, oppose or form a right angle.
Full keypad with memory and a tape — and it prints how it read your expression, so 2+3×4 shows as 2+(3×4) before you trust the 14.
What is X% of Y, reverse percentages, increase and decrease — the same maths as typing into site search.
Solve any right triangle from two known values, watch the unit circle trace sine and cosine live, and see the Pythagorean identity hold at every angle.
Area and perimeter for eight flat shapes, volume and surface area for eight solids — circles to torus, squares to spheres — each with a live, labelled diagram.
How many visitors a test really needs, the smallest effect yours could detect, and what peeking early does to the false-positive rate.
Roll d4 to d100 or flip coins as real 3D objects, with the exact distribution behind every roll — plus advantage, exploding dice, four dice that beat each other in a circle, and a chi-squared fairness test on your own rolls.
Standard deviation, z-scores and normal-curve probability — plus a real Galton board where balls fall through pegs at genuine random and build the bell curve live, differently every run.
Plot up to eight functions at once, drag to pan, scroll or pinch to zoom, and trace live coordinates along any curve — a fast, offline, Desmos-style grapher.