Your first measurement,
step by step.

01 · Before the photo

Prepare the reference stick

You need the app, a ruler or tape measure, and a flat reference with red at both ends and a checker border on all four sides. The whole stick and the object’s four corners must fit in one photo.

1. Print the reference stick at 100% / Actual size. Turn off “Fit to page”.
2. Check the printed 10 cm ruler against a real ruler. The complete reference, including the checker border, should be 20 cm long and 4 cm wide.
3. Cut along the outer border and mount it on a flat, rigid backing. Keep the checker margin and measure the full outside dimensions after mounting.
4. Place it flat against the same surface as the object. A stick held in front of a wall does not set the wall’s scale correctly.

Using your own stick? Enter its measured full length and short width. Include its checker border, but not any blank paper outside it. Do not enter the length of one coloured band.

02 · In the app

Set both dimensions

Open Settings from the camera screen. Choose your display units, then enter Reference stick length and Reference stick width.

Printed stick, centimetres

Length 20 · Width 4

The same stick, metres

Length 0.20 · Width 0.04

Use the values you actually measured. Both must be positive numbers. Settings are saved between sessions; return with the back arrow.

The “Feet & inches” setting displays results in feet and inches, but its input fields use decimal feet: 1.5 means 1 foot 6 inches. For the printed stick, entering 20 and 4 in centimetres avoids conversion rounding.

03 · Frame the surface

Take a clear photo

1. Allow camera access when Android asks. Take the photo inside Metrologist so it has the camera and tilt information for the shot.
2. Keep the whole object and reference visible, with space around their edges. Use even light; avoid blur, glare and shadows over the bands.
3. For v0.0.1, use a moderate oblique view rather than a perfectly straight-on or nearly edge-on view. Keep all corners easy to distinguish.
4. Hold the phone still and tap Capture.

The object and reference must lie on one flat plane. A door frame, raised trim or curved surface is not the same plane as the flat panel behind it.

04 · Mark the photo

Two boxes. Four corners each.

First, put the green box around the object you want to measure. Put its four dots on the object's four corners. Then adjust the red box around the stick, as shown below.

Put the red box around the whole stick

Think of the red box as a fence. Keep every checker square inside it. The four red dots go on the four outside corners, labelled A, B, C and D below. The two yellow dots halfway along the ends are not corners.

1. Zoom in with two fingers until the stick is easy to see.
2. Drag dot A to the top-left outside corner. Then place B, C and D on the other three outside corners. The letters are only in this guide; they are not printed on the stick.
3. The centre of each dot must sit where the two outside edges of the thin black line meet. Use the little magnifier to see the corner.
4. Look along all four sides. The red lines should follow the outside edges, with all the checkers inside. Then tap Measure.

The current automatic detector expects the older band pattern. For this checker design, align all four red handles manually before measuring. The initial green box is a placeholder, not a detected object.

05 · Check the reading

Understand the result

Width and height

The averages of the two opposite edge lengths. On a rectangle, these are its usual width and height.

Area

The area inside the four marked object corners. The reference stick is not added to it.

Diagonal

The average of the two corner-to-corner diagonal lengths.

Corner angles

90° describes a square corner. Start with rectangular objects; one photo cannot resolve every four-sided shape reliably.

Confidence and notes

Read the confidence label, percentage and caveats together. A high confidence score is a quality indicator, not a guaranteed error percentage.

Low confidence, a fallback-method note or inconsistent readings are reasons to check the marks and take another photo. Check important dimensions with a ruler or tape.

06 · Next action

Correct or keep the measurement

• Re-mark: return to the same photo, adjust the boxes, then measure again.
• Export: open Android’s share sheet with an annotated PNG containing the photo and measurement summary. Choose a sharing or saving app available on your phone.
• New: return to the camera for another measurement.
• On the marking screen, Retake takes a new photo; Reset restores the starting boxes and zoom, discarding your adjustments.

If the app cannot produce a usable result, correct the photo, reference dimensions or marks before exporting. Do not treat a failed or zero-sized reading as a measurement.

07 · A useful first test

Measure something you can check

Use a flat rectangular panel or board placed upright. Measure its width and height with a ruler, then repeat with the app and the reference on its face.

1. Compare the app’s width and height with the ruler values in the same units.
2. Re-mark carefully, then take a second photo from a slightly different angle.
3. If readings disagree, recheck the reference dimensions, its position and all eight handles.

Error (%) = |app value − ruler value| ÷ ruler value × 100. For example, 50.5 cm against a known 50 cm is a 1% error. This example is not an accuracy guarantee.

08 · Troubleshooting

When a measurement looks wrong