Euro sign calibration test + keyring

This is a small piece to check the calibration of you printer using a 1-Euro coin as a reference.

€1-coin specifications:
- Diameter: 23.25 mm
- Height at edge: 2.33 mm

A *tolerance of 0.2 mm has been added in the design* to both the inner diameter and the height.

Test:
- Inner diameter should fit a €1 coin.
- Distance between the middle bars is the same as the coin height.
- Middle bars height and width are the same as the coin height.
- Total height is the same as two €1 coins s