tatmapper-app

Coin and custom-round calibration

Quarter calibration is TatMapper’s recommended quick shop workflow. It is portable, familiar, and does not require printing a reference first. The Placement Card remains the perspective-correction backup when a larger four-corner reference is appropriate.

Immutable U.S. values

Coin	Diameter
Dime	17.91 mm
Penny	19.05 mm
Nickel	21.21 mm
Quarter	24.26 mm

Source: United States Mint coin specifications. The quarter is presented first and labelled Recommended because it is the largest of these common options and normally supplies more reference pixels. TatMapper does not guess a denomination.

Procedure

1. Select the denomination, or choose a custom round object and enter its measured diameter.
2. Place it flat, fully visible, and in the placement plane.
3. Keep the camera as square as practical.
4. Align four rim handles at top, right, bottom, and left.
5. Resolve any too-small, center-mismatch, or excessive-ovality warning.
6. Confirm the observed size and continue with the camera-angle warning visible.

Never enter an assumed custom diameter. Measure the actual object. The final printed 100 mm rulers remain required.

Coin scale does not correct projective perspective. If the coin appears strongly oval, the app rejects the observation; retake the photo more square to the placement plane or use the four-corner Placement Card backup.