Sensors: Compass, Level, GPS, Stopwatch and Display Tests

Six panels share one page: a Level with slope outputs, a Compass with declination, a Vibration meter, a GPS speedometer and trip computer, a lap-timer Stopwatch with countdowns, and a Display test for rulers, patterns, refresh and input. Motion, orientation and location come from device APIs; stopwatch and display work on a desktop. Each panel has its own address — level, compass, vibration, gps, stopwatch, display tests — and everything runs locally.

Updated 2026-10-01Reviewed by CalcX Editorial Team6 sources5 min read

How to use it

Pick a panel.The strip switches between the six; each panel's address loads it directly.
Start it and grant access when asked.On iOS 13+ the motion and orientation request must happen inside the tap, so Start triggers it; GPS asks for location. Deny it and the panel explains how to re-enable; the level's manual converter and the screen panel still work if a sensor is missing.
Level and compass.Lay the phone down, Set zero to cancel case and table tilt, read pitch, roll and total tilt (Hold freezes). On the compass choose Magnetic or True north; coordinates and a declination override are editable.
GPS and vibration.Start GPS for speed, altitude, heading while moving, fix age, trip distance, max/avg speed. Start vibration for RMS, peak, peak hold, crest factor, dominant frequency and sample rate.
Stopwatch and display tests.Lap records split, total and the change from the previous lap; countdowns survive a reload. The display panel calibrates a ruler with a bank card, then offers a protractor, eight patterns, refresh, touch and key tests.

Worked readouts

The angle, ruler, protractor and stopwatch rows reproduce on any device with the same input.

Panel	You enter	The page reads
Level, manual converter	5°	8.749 %, ratio 1:11.4, 87.27 mrad
Level, manual converter	45°	100.000 %, 1:1, 785.40 mrad
Compass, default 39.9042 N, 116.4074 E	—	declination +1.70° E, geomagnetic latitude 30.71°
Screen ruler, 96 dpi	100 px	26.46 mm; 25.4 mm reads 96.0 px
Protractor	default handles	included 115.69°, supplement 64.31°, 2.0191 rad, 128.54 gon
Stopwatch, three laps	12.34 / 25.00 / 40.00 s	splits 00:12.34 best, 00:12.66, 00:15.00 worst; changes +00:00.32, +00:02.34
Vibration, a 10 Hz, 2 m/s² tone	—	RMS 1.414 m/s², peak 2.000, crest factor 1.41, dominant 10.02 Hz

GPS converts on its own line: 10 m/s reads 10.00 m/s, 36.0 km/h, 22.4 mph.

How the panels read the device

The browser abstracts hardware, so every reading is a sample with provenance. The level prefers orientation angles and falls back to accelerometer tilt after events go quiet for a second, showing gravity magnitude (~9.8 m/s² at rest). The compass smooths along the shortest arc: 350° then 10° moves through 355°. The stopwatch runs on a monotonic clock, so a throttled tab cannot drift.

Limits

Consumer hardware, honest labels.: Level resolution is roughly 0.1–0.5°; accelerometers span about ±2–8 g at 50–100 Hz; magnetometers are disturbed by mounts, speakers and metal. The vibration panel prints its usable band and Nyquist limit.
A fix is an estimate, not a satellite list.: The Web Geolocation API exposes a confidence radius and no satellite count, HDOP or fix source, so a "satellites locked" readout is impossible. Indoors it usually falls back to Wi-Fi or cell towers, with speed and heading null, and fixes coarser than 50 m are dropped from the trip.
It is not a navigation or analysis suite.: No maps, routing or seismograph, no angle or speed conversion beyond each panel's readouts — those live in the angle converter, the speed converter and the uncertainty toolkit.

The heading is not a bearing

True heading rides on a dipole approximation. The default declination is a centred dipole (IGRF-2020 pole at 80.7° N, 72.7° W): at the default coordinates it reads +1.70° E, but the panel's own note warns the model is typically a few degrees off at mid-latitudes and up to about 10° in East Asia. Type a NOAA value into the override, or open the WMM lookup.
Relative orientation has no magnetic north. When the card reads Absolute reference no (drifts), alpha only knows where the page started: move away from metal and wave the phone in a figure-8 to recalibrate.

Where it helps

Hanging and levelling

Set zero against a surface you trust, then read pitch and roll — 8.749 % and 1:11.4 at 5°, 21.256 % at 12°. The manual converter needs no sensor.

Walking, cycling and driving

The dial shows 10 m/s as 36.0 km/h and 22.4 mph, accumulates trip distance between fixes, and reports max and average speed. Heading stays empty while stationary.

Testing a phone or a monitor

Solid fields expose dead pixels and bleed; grey steps show banding; the refresh measurement reports the presented frame rate, which can sit below the panel's spec. Touch finds dead zones; the key tester prints the character beside the key code.

References

W3C, Device Orientation and Motion, w3.org （访问日期：2026-10-01）— alpha, beta and gamma, the compass-heading relation (360 − alpha) and the permission model.
W3C, Geolocation, w3.org （访问日期：2026-10-01）— accuracy as a radius, speed, heading and the high-accuracy hint.
ISO, ISO 2631-1:1997, Mechanical vibration and shock — Evaluation of human exposure to whole-body vibration, iso.org （访问日期：2026-10-01）— the comfort threshold behind the perception table.
ISO, ISO/IEC 7810:2019, Identification cards — Physical characteristics, iso.org （访问日期：2026-10-01）— the ID-1 bank card, 85.60 × 53.98 mm, behind the ruler calibration.
NOAA NCEI, World Magnetic Model WMM2025, ncei.noaa.gov （访问日期：2026-10-01）— the model behind the declination lookup.
MDN Web Docs, Performance.now(), developer.mozilla.org （访问日期：2026-10-01）— the monotonic clock behind the stopwatch.