Full instruments
The sextant.
Celestial · offlineA working nautical almanac and sight reduction computer that needs no signal. An auto mode walks the whole procedure and puts an artificial horizon over the camera; or shoot by hand with the phone's inclinometer, or type in a reading from a real sextant, and get a position by least squares. Install it to the home screen and it runs with the radio off.
The listening post.
Signals · WebUSBA browser has exactly one wideband receiver, the microphone, and everything else is walled off on purpose. So this probes what the device will actually let a page hear, puts a real analyzer on the band you do get, and drives an RTL-SDR over WebUSB for the rest.
The optical bench.
Camera · metrologyThree instruments that treat the camera as a photometer. A photon transfer curve for what the sensor's noise is made of and how many stops it really has, a slanted edge for what the lens actually resolves, and Beer-Lambert absorbance with a calibration curve for what is dissolved in a cuvette.
The dive planner.
DecompressionBuhlmann ZH-L16C with gradient factors, the algorithm inside a modern dive computer, written out where you can watch it work. Sixteen tissue compartments loading and off-gassing, a live ceiling, a stop schedule, and the gas planning that decides whether any of it is survivable. It also keeps a dive log on the device: import what your computer's app exports, build a profile by dragging it, and take it away as a spreadsheet. A teaching instrument, not a dive computer.
The visualiser.
Audio · WebGLTwelve ways to look at the same sound, full screen and built to be stared at. Nine of them are a spectrogram displaced on the GPU, so frequency across, time toward you and level as height becomes a landscape, a tunnel, a canyon, a mandala, a planet, a torus, a whirlpool, a twisting ribbon, or a flat torus in four dimensions that squares off into a tesseract and turns through itself. The other three draw the geometry the notes have rather than the spectrum does: pitch as a helix where one turn is an octave and a chord is a shape you can recognize, rhythm as a spectrum of how fast each band is pulsing, and the stereo image with time running away from you. Feedback trails, bloom and chromatic aberration on top, driven by an onset detector. Every height is still a measurement, and the maths is written out in the page.
The exoplanet census.
Astronomy · live dataEvery confirmed planet outside the solar system, pulled live from the NASA Exoplanet Archive by your own browser. The points are the easy part. The interesting thing is the empty regions, because most of them are empty for reasons that have nothing to do with what is out there: turn on the transit depth, transit probability and radial velocity contours and the boundaries of the sample land exactly on lines drawn by our instruments. The radius valley and the Neptune desert are both in here, along with everything derived from first principles rather than read from a column.
The room tuner.
Acoustics · micMeasure a room properly. A swept sine deconvolves to the impulse response, which gives reverberation time per octave to ISO 3382, the frequency response, and where your predicted modes actually landed. An auto mode runs the whole sequence and reads the result back in plain terms. Then it tells you what to fix, and refuses to pretend EQ can fix all of it.
Games
The swimmer.
Biophysics · gameA flight simulator for a bacterium. At Reynolds number 0.0001 water behaves like tar, inertia does not exist, and every instinct you have about moving through a fluid is wrong: stop swimming and you stop dead within the width of an atom. Purcell's scallop theorem is here to be failed at, then beaten with a corkscrew. Then you steer a cell to a sugar source the only way a cell can, by choosing when to give up on a direction, and race twenty four of them that do it properly.
The bloodstream.
Haemodynamics · gameYou are a nanoparticle in a small artery, with no engine, no rudder and sixteen forks between you and the tissue. The tree is built from Murray's law alone and every number falls out of it: the velocity, the wall shear that barely moves in sixteen generations, and the fact that blood in a capillary flows almost as easily as water. At each fork the fluid has already decided, and all you can do is be on the right side of the dividing streamline when you arrive. Then get to the wall and try to stick before the shear tears you off.
Live & interactive
Waterfall.
Spectrogram · micA full FFT waterfall, frequency across, time falling down, loudness in the palette. Point it at a stack and watch the sub-bass bloom.
Spectrum analyzer.
Signal · micLive microphone FFT on a log axis, room modes, tuning, and the mains hum you pretend not to hear.
The tuner.
A = 440Chromatic, play a note, the needle does the judging. Audio never leaves the browser.
Kármán vortex street.
CFDA live D2Q9 lattice-Boltzmann fluid shedding vortices past a cylinder, the Strouhal number, caught in the act.
Reaction–diffusion.
TuringGray–Scott: two reactants diffuse and react until spots, stripes, and coral emerge from noise.
Fourier epicycles.
DFTDraw a closed shape with a finger. Its Fourier transform turns it into a stack of rotating circles, each turning a whole number of times per lap, and the pen on the end retraces exactly what you drew.
Double pendulum.
LyapunovTwo pendulums launched a hundred millionth of a radian apart. Watch how long they agree, then watch the exponent that measures exactly how fast they stop agreeing.
Fractal frost.
AggregationParticles wander in from nowhere and stick where they first touch. Tips catch wanderers before the hollows do, so tips grow, and the result is a fractal that measures its own dimension.
The Ising model.
Phase transitionSpins on a lattice, each one only wanting to agree with its neighbours. Drag the temperature down through the critical point and watch order appear out of nothing.
Quantum tunnelling.
SchrödingerA Gaussian wavepacket thrown at a barrier it does not have the energy to cross. Some of it goes through anyway. Split-step Fourier, solving the real time-dependent equation.
Chladni figures.
ModalSand on a driven plate, walking away from the antinodes until it is stranded on the nodal lines. Sweep the frequency by hand, or let the microphone drive it and sing at the plate.
Harmonograph.
LissajousTwo frequency ratios, four damped pendulum swings. Signal processing that thinks it's jazz.
Chem & pharma
Pharmacokinetics.
Half-lifeSteady-state accumulation for repeated dosing, where the drug piles up, and when it stops.
Buffer pH.
Henderson–HasselbalchpH from pKa and the conjugate base/acid ratio, or solve the ratio for a target pH.
Dilution & molarity.
Bench mathC1V1 = C2V2, or grams to molarity. Leave one field blank (or 0); I solve for it.
Engineering & sound
Dimensionless numbers.
TransportThe ratios that run the universe, pick one.
Engineer's converter.
UnitsPressure, temperature, flow, viscosity, the ones that actually come up.
Sound & space.
AcousticsFrequency ↔ note ↔ wavelength, and your room's first standing waves.
Photography & optics
Below the waterline.
OpticsPressure, light, color, gas, and time, the physics of a dive.
Chasing light.
SolarSunrise, sunset, and golden hour for any spot on Earth.
Flicker meter.
Rolling shutterYour sensor scans rows in sequence, so a flickering light writes stripes into a single frame. Read the stripe pitch and you have the flicker frequency of any lamp, screen or LED, plus how deeply it modulates, judged against the standard that says whether it will give people headaches.
Depth of field.
OpticsHyperfocal distance and the sliver of the world that lands sharp.
Kitchen
Espresso dial-in.
CFD dept.Enter a shot; get ratio, flow, and what to change next.
The cooling curve.
ThermoNewton's law of cooling, when is it actually drinkable?