The A0 paper format is defined as 841mm × 1189mm. To determine the image size of a 1.00 mm object, additional information such as distance or magnification is required.
The size of an A0 paper format, as defined by the international standard ISO 216, is 841mm × 1189mm. This standard of paper sizes is based on a scaling system that maintains the aspect ratio of the sheets as they are divided or enlarged.
Regarding the size of an image of a 1.00 mm object, such as lettering inside a ring, additional information is required to provide an accurate answer, such as the distance from the viewer or the magnifying equipment used.
Without these parameters, it's not possible to determine the size of the image produced.