TeslaGauger : Magnetometer

Most magnetometer apps show you a number. This one remembers where you were standing.

Walk a room with your phone and every reading is recorded WITH ITS POSITION, so a walk becomes a map. Come back next month, walk it again, and the app shows you the difference — blue where the field fell, red where it rose, white where nothing changed beyond the noise.

WHAT IT MEASURES, AND WHAT IT DOES NOT

This app measures the STATIC magnetic field: the Earth, magnets, magnetised steel. Anything that is not alternating.

It does NOT measure the 50/60 Hz field around mains wiring. The sensor converts about a hundred times a second, too few to follow a 50 Hz wave — so every reading averages a tenth of a second, which cancels the mains instead of letting it pass for something real. Not all of it: some appliances, a microwave oven for one, leave a slow swing no averaging can remove — so the app watches for running mains, tells you when the phone is near it, and marks those readings.

So no reading here is ever set beside a mains exposure limit, and nothing in this app is scored against a health threshold. What it gives you instead is a figure you can check: every measurement carries its own uncertainty, and the app withholds an absolute value until it has earned one.

WHAT YOU CAN DO

• Track — where you walked and what you read along the way
• Heat map — the room as a field, filled in between your steps
• Volume — the same in three dimensions, for sweeping around an object
• Room plan — walls and openings, on iPhone Pro (LiDAR)
• Compare — two visits differenced, with the noise threshold widened by the app's own positional uncertainty
• Export — CSV always, GeoJSON outdoors, raw and corrected side by side

AND SOMETHING TO LEARN

A course in four steps, sixteen lessons, from "a field is an arrow at every point" to what a survey crew actually does. Sixteen experiments to run yourself with the phone in your hand — including one that has to fail, and teaches you why.

WHAT IT COSTS

Everything works without paying: the readings, the maps, the room scan, comparing two visits, and the export. What the free version does not do is remember — recordings last until you quit.

Three one-time purchases, no subscription, no account:
• Keep your readings — recordings survive quitting, no limit on places or surveys
• Read them across time — play a place across every visit, plus the course, the experiments and more stories
• Write down what you measured — a PDF record of each place: every survey's heat map and strongest spots, what changed between visits, the exact handset, the calibration, the uncertainty on every figure, and the instrument's limits printed at the top

Before buying the third, every place shows its record as a free preview, stamped, on your own readings.

PRIVACY

Nothing leaves your phone. No account, no server, no analytics, no advertising. The camera is used for indoor tracking and never recorded; location is used to place outdoor readings on a map and never transmitted.

Thirteen languages, switched inside the app without restarting.

TeslaGauger is a measuring instrument, not an expert appraisal. It is not calibrated against a traceable standard, and it says so — in the app, and on every page it prints.