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Measurement field note

How to Check Plumb and Level With Your Phone: SIMT's Plumb Bob

A real plumb bob is a weight on a string that shows exactly where down is. SIMT puts one in your phone: a 3D pyramid that hangs along Earth's gravity vector and tells you, to a fraction of a degree, whether a wall is plumb, a counter is level, or a frame hangs straight — with no internet, no spirit level, and no magnetometer to fight.

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A phone displaying a tilted 3D pyramid plumb bob with pitch and roll readouts, beside a level reference showing a wall being checked for verticality.

Quick summary

  1. SIMT's Plumb Bob turns the compass screen into a 3D plumb line: a pyramid hangs along Earth's gravity vector, so you can see at a glance whether a surface is vertical, horizontal, or tilted — fully offline.
  2. The readout shows pitch and roll in degrees from a calibrated zero, and a near-level glow lights up when the surface is within a small tolerance of level.
  3. It uses the gravity sensor (gyroscope plus accelerometer fusion), not the magnetometer — so magnetic interference from steel, wiring, and appliances can't corrupt the measurement, and tilt never fights the compass heading.
  4. SET ZERO on a known-good surface turns Plumb Bob into a comparison tool: mark any reference angle, then check anything else against it; RESET TO WORLD returns to absolute gravity.
  5. It is a precision DIY tool, not a survey instrument: hold still for a stable reading, rest the phone flat on the surface, and expect home-improvement accuracy rather than construction-grade tolerance.

The short answer: a digital plumb line in your phone

The classic plumb bob — a pointed weight on a string — has hung from builders' hands for thousands of years because it answers one question perfectly: which way is down? Gravity does the work; the string simply shows it. Your phone carries an even better tool: sensors that measure the gravity vector directly, tens of times a second, with no string, no swing, and no need for a reference edge to hang from.

How a digital plumb bob works

SIMT's Plumb Bob reads the gravity sensor, a fusion of the gyroscope and accelerometer, to know exactly where down is relative to your phone. It renders that vector as a 3D pyramid: the apex stays fixed in the centre of the screen while the base hangs along gravity, exactly as a real bob hangs from its anchor point. The motion passes through a spring–damper filter, so the pyramid eases into place like a physical bob instead of jittering with every hand tremor.

Two design details make it trustworthy. First, it is pure gravity — no magnetometer involved — so nearby steel, wiring, and appliances cannot pull the reading sideways the way they can pull a compass needle. Second, it is calibratable: tap SET ZERO on a surface you know is correct, and every reading becomes a comparison to that reference; tap RESET TO WORLD to return to absolute gravity at any time.

What you can check around the house and in the field

  • Walls and wardrobes — rest the phone flat against a surface to confirm it is truly vertical (plumb), not just 'looks straight'.
  • Counters and shelves — set the phone on top to check for a level surface before fixing a shelf, rack, or worktop.
  • Picture frames — check the top edge before committing to the nail; no more re-hanging after the third squint.
  • Tripods and camera rigs — level the head before a time-lapse, a long exposure, or an astrophotography session.
  • Phone mounts and stands — verify the mount is level so the framing stays square.
  • Slopes and falls — read the exact pitch and roll of a ramp, a driveway, a deck, or a pipe that needs a deliberate fall.

The Plumb Bob pairs naturally with the rest of the compass suite: the HUD readout shows pitch and roll as angles for the same orientation the compass is already resolving for heading, and the red rim dot still marks magnetic north — so you can measure a surface's tilt and its orientation in one glance, with one app, offline.

How to use it, step by step

  1. Open SIMT's compass and swipe to the Plumb Bob view.
  2. Hold the phone still for a second or two — the spring–damper filter needs a moment to settle the pyramid, just like a real bob.
  3. Rest the phone flat or flush against the surface you are checking, back or edge against it for best contact.
  4. Read the numbers — the HUD shows pitch (forward–back tilt) and roll (side-to-side tilt) in degrees relative to your zero.
  5. Watch for the near-level glow — the surface is considered effectively level when the reading is within a small tolerance of your reference.
  6. Use SET ZERO on a surface you know is correct to make the tool a comparator: anything you check afterwards reads as the difference from your reference.
  7. Tap RESET TO WORLD when you are done comparing, so the next session starts from absolute gravity again.

For the fullest picture, combine views: verify a surface is level with Plumb Bob, confirm the heading it faces with the compass, and if you need dimensions rather than angles, the Measure screen handles distance, area, and diameter on the same phone.

Keep reading The same phone that checks your shelves can measure a ring size, a room, or a diagonal — here is the full Measure toolkit.How to Measure a Ring Size With Your Phone (No Ring Sizer Needed) You want to buy someone a ring as a surprise. You obviously can't ask for their finger size. But you can borrow a ring they already own for thirty seconds — and your phone can turn that ring into a number. Here is how SIMT's Measure tool makes your screen a calibrated caliper, and everything else it can measure once you have it open.

Honest limitations: DIY precision, not survey grade

Plumb Bob is a genuinely useful field tool, and it is honest about its limits. Consumer phone sensors deliver home-improvement accuracy — perfect for frames, shelves, and camera rigs, but not a substitute for a surveyor's level when tolerances are measured in millimetres over metres. Always rest the phone on a flat, stable surface and hold still while reading; the numbers reflect the surface you touch, not the wall behind it. And if the surface itself is curved or warped, so is the measurement.

When you need it, it works — offline

Plumb Bob runs entirely on the sensors in your hand: no network, no account, no server round-trip. Use it in a basement with no signal, in a garage full of steel, or on a rooftop at night — the reading is identical. It is one more reason the toolkit works in the places other apps stop: plan with targets, navigate with the compass, and verify with Plumb Bob — all offline, all private, all in one app.

A weight on a string taught builders where down is for thousands of years. Your phone already knows — SIMT just lets you see it.

Get SIMT — free on Google PlayPlumb Bob, Measure, Ray+, and the compass suite — a measurement toolkit that never needs a signal.

Questions answered in this guide

What is a plumb bob, and what does SIMT's version do?

A plumb bob is a weight on a string that shows the direction of gravity — the classic way to establish true vertical. SIMT's Plumb Bob is the digital equivalent: a 3D pyramid that hangs along Earth's gravity vector, showing you in degrees whether a surface is plumb (vertical), level (horizontal), or tilted.

Does Plumb Bob use the compass or the magnetometer?

Neither for the measurement itself. It uses the gravity sensor — a fusion of the gyroscope and accelerometer — so magnetic interference from steel, wiring, or appliances cannot skew the reading. The red rim dot still marks magnetic north, but tilt and heading are measured independently.

How accurate is it?

Accurate enough for home and field use: hanging frames, checking shelves, levelling tripods, and measuring slopes in degrees. It is not a survey instrument — for construction-grade tolerances measured in millimetres over metres, use a proper level. Hold the phone still on a flat surface for the steadiest reading.

How do I calibrate Plumb Bob?

Tap SET ZERO while the phone rests on a surface you know is correct (a level counter or a plumb wall). Every reading afterwards shows the difference from that reference. Tap RESET TO WORLD to return to absolute gravity, measured directly from the sensors.

What are pitch and roll?

Pitch is the forward–back tilt of the phone relative to your reference, and roll is the side-to-side tilt — both shown in degrees in the Plumb Bob HUD. At zero in both, the surface matches your reference: level if the phone is face-up, plumb if it is held flat against a vertical surface.

Does Plumb Bob need an internet connection?

No. It runs entirely on your phone's gravity sensors, so it works with full signal, weak signal, or no signal at all — in basements, garages, and remote sites where other tools give up.

Can I measure the angle of a slope or a pipe?

Yes. Rest the phone on the surface and read the pitch and roll directly — a ramp, a driveway, a deck, or a pipe that needs a deliberate fall. Use SET ZERO on the reference angle first if you need a comparison rather than an absolute reading.

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