You would like to determine your real magnification but a normal ruler is not exact enough? This micrometer calibration tool has 1/10mm (0.1mm) markings on the glass. The tool comes together with a plastic case.
Within the EU, the goods usually arrive within a few working days. Deliveries outside of the EU can take from just over a week to two weeks. Even an exchange or return within 14 days can be handled more quickly, less complicatedly, and more cheaply via the MJKZZ.DE page, if the goods only need to be sent back to Germany/Austria.