Some OMR sheets are printed on both sides. These sheets are otherwise referred to as duplex sheets. These sheets fairly complicated in structure and have OMR blocks on either sides of the sheet. Irrespective of whether there are OMR bubbles both sides OMR duplex printing must be done based on a few set guidelines which are explained as below.
For duplex printing, the paper should be adequately thick, to ensure that the printing impression on one side is not carried over to the other side. In case, the paper used is thin, then it will absorb the printing on one side and will show on the other side of the paper. And, this will cause problems because even a small impression of the ink will get scanned as mark, during the scanning of OMR sheets. And, this will be treated as a response.
Another important precaution to be taken is during offset printing. If the sheets are stacked in a pile over each other, then there will not be enough time for drying. Even though, its not a new thing with offset printing and it usually works like that, but OMR sheets require more care. If it were normal paper, a little bit of smudging here are there will not cause issues, but with OMR sheet, the smudging will cause impressions in wrong places and will affect the scanning and reading process. So, while doing duplex printing, bold color patches should not be used on any of the sides. These bold and dark patches take a longer time for drying up. In case of duplex printing, one should use only thin borders for the lines, leaving no room for the smudging of wet ink.
Another point to be noted is that the index points should be there on either sides. But, if you are designing the Duplex OMR with the help of Addmen OMR software, then it becomes quite easy as there is no need for doing the perfect matching of girds on either sides. There can be separate OMR designs on both the sides of paper. The OMR Reader will be able to read both side and will be able to present them as a combined result.