OMR sheets are used for conducting MCQ based examinations, with bubbles or checkboxes provided for marking the answers to the questions. While solving certain numerical questions, you might need to do some rough work to solve the question and obtain the answer. But never do rough work on the OMR sheets themselves. Remember that OMR sheets are evaluated by the OMR software or an OMR scanner machine; so any stray marks on the OMR sheets will disrupt the OMR reading process.
Addmen OMR software reads black/dark marks from the OMR sheet, and it uses the four index points on its corners to calibrate the sheets for reading and processing the results. However, any rough work done on these sheets would appear as stray markings to the OMR reader and thus may result in rejections or may need manual evaluation.
Some students have the habit of writing slogans or holy salutations on their exam papers. Never do this in OMR examinations; as such text will also confuse the OMR reader. Handle the OMR sheets with care, and keep them off of stray ink marks, scratches, and dirt marks.
Any rough work must be done on an extra paper which you can request from the examination invigilator. Although the Addmen OMR software is designed to read black marks from specific areas of the sheet, you need to make sure there are no stray marks, just to avoid any chances of rejections during the evaluation process, as you do not know if the exam body uses any other OMR software or an OMR scanner machine, in which case stray marks can cause disruptions in the reading process.