All candidates must ensure they fill all the details in the candidate details section properly, before starting to solve the test sheet. The OMR software used to evaluate the sheets specifically reads dark marks from the OMR sheet and compares it to the answer key. Candidates are required to enter their roll no in the OMR bubble format, as well as in written format. Handwritten roll number will not be processed by the OMR answer sheet checking software; it registers the roll number in OMR format only. It is imperative that you fill your roll number in OMR format, as it is what the examination body relies on to conduct automatic evaluation, without manually checking or administering the candidate details for each paper.
OMR sheet checking software prompts for manual validation if it fails to read the roll no. If you have forgotten to fill your roll no. in OMR format, but have written it in the box provided; then evaluators can fill the bubbles manually by referring to the written format. But as you may know, evaluating thousands of sheets might be subject to time constraints, and certain examination bodies might not entertain such needs. Hence, it is critical that you first fill your roll no. carefully upon receiving the answer sheet.
Some candidates are observed to immediately start solving the question paper and start marking the answers, without filling the candidate section first. Although they might be anxious to get solve all the questions and secure more scores, they might not get enough time for that if they wait till the last moment. It is advisable that candidates fill their details first, and then proceed to solve the questions. Missing out on a couple questions may only cost you a few marks, but forgetting to fill the roll no. might get you rejected during evaluations.