RulerPhone was an iPhone measurement app by Ben Kamens. The archived August 29, 2008 listing describes using a photograph and an object the size of a credit card as the reference for measuring something else in the frame.
This is a reconstruction of that historical method. It does not verify current download availability or establish the app’s accuracy on any particular object or phone.
The reference gives the picture meaning
A photograph contains apparent sizes. A known reference is what gives a photo-measurement tool a basis for relating the image to a physical dimension. Without knowing what the reference represents, a precise-looking number can be difficult to interpret.
When assessing this kind of tool, ask how it expects the reference and target to be positioned. A photograph is a view from one position, not a flat technical drawing. The app’s instructions need to explain which assumptions make its calculation useful.
Decide which dimension you need
Before taking a picture, identify the two endpoints of the measurement. The visible front edge of a piece of furniture and its deepest projecting part may answer different questions. A clear image of the wrong dimension is still the wrong evidence for a fit decision.
For an initial comparison, keep the original photograph with the result. That allows you to revisit which edge was selected and whether the reference was clearly visible. A number separated from its image is harder to check later.
An estimate and a final fit are different tasks
The original listing suggested uses such as apartment hunting and shopping for furniture. Those examples explain the convenience of having a measurement tool in a camera-equipped phone; they do not prove that every use has the same tolerance for error.
If an exact fit matters, verify it with an appropriate direct measurement before committing. RulerPhone’s historical identity is specific: Ben Kamens’ reference-based photo tool, rather than a later augmented-reality measuring app with a similar purpose.