In short: CBSE's On-Screen Marking (OSM) system scans your Class 12 answer sheet and displays it on an examiner's screen. What looks fine on paper may not scan well. What you assume the examiner will understand, they may not see. These 20 insights — drawn from examiner accounts, CBSE's own OSM guidelines, and the 2026 re-evaluation controversy — tell you exactly what to do differently.
Last updated: October 29, 2026. OSM continues for CBSE Class 12 in 2027. Source: CBSE official OSM guidelines.
Background: What OSM Actually Is
CBSE piloted On-Screen Marking for Class 12 from 2019 and expanded it progressively. Under OSM, answer sheets are scanned at the exam centre and uploaded to a central server. Examiners evaluate the scanned images on their computer screens from home or a designated centre.
The 2026 expansion to near-full scale had significant problems. Students reported blurred scans, unchecked pages, and missed step marks. A large number of answer scripts were requested for re-evaluation — an unprecedented volume that strained the system. CBSE defended the system but acknowledged implementation issues. (Business Today, Indian Express)
OSM continues for 2027 with improvements. Understanding how it works — and what examiners actually see — is now essential exam preparation.
The 20 Insights
1. Dark ink scans; light ink disappears
The scanner captures contrast. Dark blue or black ink on white paper produces a high-contrast image that scans clearly. Light blue ink, pencil, or faded pen produces a low-contrast image that may appear washed out on screen.
What to do: Use a dark blue or black ballpoint pen. Test your pen before the exam — press firmly on a piece of paper and check that the ink is dark and consistent. Do not use gel pens that smear or fountain pens that produce variable ink density.
2. The examiner sees a screen, not a sheet
When you write on paper, you have a sense of the whole page — the layout, the spacing, the flow. The examiner sees a digital image on a monitor. The image may be zoomed in or out. What looks well-organised on paper may look cluttered on screen.
What to do: Write larger than you normally would. Leave more space between lines. Use wider margins. The examiner should be able to read your answer without zooming in.
3. Page edges are the most common scan failure point
The scanner captures the full page, but the edges — especially the left margin and the bottom of the page — are the most likely to be cut off or blurred in a scan. Content written in the margins or at the very bottom of a page is at risk.
What to do: Keep all writing within the printed margins of the answer sheet. Do not write in the margins. Do not write below the last printed line on a page. Leave a 1 cm buffer from all edges.
4. Step marking requires visible steps
In Maths, Physics, and Chemistry, marks are awarded for each step of a solution — not just the final answer. Under OSM, the examiner must be able to see each step clearly on screen to award step marks.
In 2026, the most common complaint in re-evaluation requests was missed step marks — examiners who could not clearly read intermediate steps on screen and therefore did not award them. (Indian Express)
What to do: Write each step on a new line. Do not compress multiple steps onto one line. Label each step if the subject allows it (e.g., "Step 1: Apply KVL"). Even if you are short on time, write the key steps — a partial solution with visible steps earns more marks than a correct final answer with no working shown.
5. Diagrams must be drawn in pen, not pencil
Many students draw diagrams in pencil and label them in pen. Under OSM, pencil lines scan poorly — they appear faint or disappear entirely on screen. An examiner who cannot see your diagram cannot award marks for it.
What to do: Draw all diagrams in pen. Use a ruler for straight lines. Label clearly in pen. If you make a mistake in a diagram, cross it out neatly and redraw — do not erase (erasing leaves marks on the paper that scan as smudges).
6. Crossing out must be a single clean line
When you cross out a mistake, use a single horizontal line through the text. Do not scribble over it, do not use correction fluid (not allowed), and do not use multiple overlapping lines. Heavy scribbling creates a dark blotch on the scanned image that can obscure nearby text.
What to do: One clean horizontal line through the text you want to cancel. The examiner will ignore it. If you scribble heavily, the scan may show the scribble obscuring the correct answer you wrote next to it.
7. Question numbers must be clearly visible
Under OSM, examiners are assigned specific questions to mark — they do not mark the entire paper. They see only the pages containing their assigned question. If your question number is unclear, the examiner may not be able to identify which question you are answering.
What to do: Write the question number clearly at the start of each answer, in the margin or in the designated space. Circle it or underline it. Do not assume the examiner will figure it out from context.
8. Sub-parts must be clearly labelled
If a question has sub-parts (a), (b), (c), each sub-part must be clearly labelled. Under OSM, the examiner may be marking only one sub-part and needs to find it quickly on the scanned page.
What to do: Write (a), (b), (c) clearly at the start of each sub-part. Leave a line gap between sub-parts. Do not run sub-parts together.
9. The examiner cannot flip back to check your earlier work
In manual checking, an examiner can flip back through your answer sheet to check an earlier answer. Under OSM, the examiner sees a digital image and may not have easy access to earlier pages. Each answer should be self-contained.
What to do: Do not write "as shown earlier" or "refer to Q3." Repeat the relevant information if necessary. Each answer should make sense on its own.
10. Blank pages are not automatically checked
In 2026, one of the most serious complaints was unchecked pages — pages that were blank or nearly blank and were therefore skipped by the system or the examiner. If you leave a page blank and continue on the next page, the blank page may cause the examiner to miss the continuation.
What to do: Never leave a page completely blank in the middle of your answer. If you need to continue on the next page, write "Continued on next page" at the bottom of the current page. If a page is genuinely blank (you skipped it), draw a diagonal line through it and write "Blank."
11. Continuation must be clearly marked
If your answer continues on a later page (because you ran out of space), you must clearly indicate this. Under OSM, the examiner may not see the continuation if it is not clearly linked.
What to do: At the end of the page, write "Q[number] continued on page [X]." At the top of the continuation page, write "Q[number] continued." This creates a clear link that the examiner can follow.
12. Graphs and tables must have clear labels
Graphs in Economics, Biology, and Physics are frequently tested. Under OSM, a graph that is not clearly labelled — axes, units, curves — may not earn full marks even if the shape is correct.
What to do: Label both axes with the variable name and unit. Label each curve or line. Mark key points (equilibrium, intercepts) clearly. Use a ruler for straight lines. Write labels in pen, not pencil.
13. The examiner has a time limit per answer
Under OSM, examiners are typically given a target number of scripts to evaluate per day. This creates time pressure. An answer that is easy to read and clearly organised will be evaluated more carefully than one that requires the examiner to work hard to understand.
What to do: Use headings and sub-headings where appropriate. Use bullet points for lists. Leave space between paragraphs. Make the examiner's job easy — it directly benefits you.
14. Overwriting is a scan problem
Writing over a word to correct it — pressing harder to make the correction visible — creates a dark, blurry mark on the scanned image. The examiner may not be able to read either the original or the correction.
What to do: Cross out the mistake with a single line and write the correction next to it or above it. Do not overwrite.
15. The answer booklet cover page matters
The cover page of your answer booklet — where you write your roll number, subject, and other details — is scanned and used to identify your script. If this information is unclear or incorrect, your script may be misidentified.
What to do: Fill in the cover page carefully and completely before the exam starts. Write your roll number in block letters. Double-check it against your admit card.
16. Ink that bleeds through the page creates problems
Some pens — particularly cheap ballpoints with thin paper — cause ink to bleed through to the back of the page. Under OSM, this creates ghost images on the scanned page that can obscure text.
What to do: Test your pen on the answer sheet paper before the exam if possible. Use a pen with consistent, non-bleeding ink. Press firmly but not so hard that the ink bleeds through.
17. Long answers need internal structure
For 5-mark and 6-mark answers, examiners are looking for specific points from the marking scheme. Under OSM, a long paragraph with no structure is harder to evaluate than a structured answer with clear points.
What to do: Use numbered points or bullet points for long answers. Each point should correspond to one mark. This makes it easy for the examiner to award marks systematically.
18. The marking scheme is the examiner's guide
CBSE examiners mark against the official marking scheme, which specifies exactly which points earn marks. Under OSM, the marking scheme is displayed alongside the scanned answer. The examiner is looking for specific keywords and concepts.
What to do: Use the language of the textbook and the marking scheme. If the marking scheme says "the rate of reaction increases with temperature," write exactly that — do not paraphrase in a way that might not match the expected answer.
19. Re-evaluation is possible but takes time
If you believe your answer was not evaluated correctly under OSM, you can apply for re-evaluation. In 2026, 11 lakh students applied. The process involves: (1) applying for a scanned copy of your answer sheet, (2) reviewing it, (3) applying for verification, and (4) applying for re-evaluation if you still believe there is an error.
What to do: Know that this option exists. But the best strategy is to write in a way that does not require re-evaluation — clear, dark, well-organised answers that are easy to evaluate correctly the first time.
20. Practice writing for a scanner, not for a reader
The fundamental shift OSM requires is this: you are no longer writing for a human who will hold your paper. You are writing for a scanner that will photograph your paper and display it on a screen. Everything about how you write — pen choice, pressure, spacing, margins, diagram style — should be optimised for this.
What to do: In your mock exams and practice sessions, write as if your paper will be scanned. Use dark pen. Write larger. Leave margins. Draw diagrams in pen. This is not just exam technique — it is the new reality of CBSE Class 12 evaluation.
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The 2026 OSM Controversy: What Went Wrong and What Changed
| Problem reported in 2026 | CBSE's response | Change for 2027 |
|---|---|---|
| Blurred scans at some centres | Acknowledged; attributed to scanner quality | Upgraded scanners at all centres |
| Unchecked pages | Denied by CBSE; disputed by students | New protocol: every page must be marked as checked |
| Missed step marks | Attributed to examiner error | Additional examiner training on step marking |
| 11 lakh re-evaluation requests | Unprecedented; system strained | Faster processing; additional evaluators |
Source: Business Today, NDTV.
CBSE's position: "Only the medium has changed, not the marking." The system continues for 2027 with the improvements listed above.
Quick Reference: OSM Writing Rules
| Rule | Why It Matters |
|---|---|
| Dark blue or black pen only | Light ink scans poorly |
| Write within margins (1 cm buffer from edges) | Edges are most likely to be cut off in scan |
| Each step on a new line | Step marks require visible steps |
| Diagrams in pen, not pencil | Pencil scans faintly or not at all |
| Single clean line to cross out mistakes | Heavy scribbling obscures nearby text |
| Question number clearly written and circled | Examiners mark specific questions, not full papers |
| "Continued on page X" for long answers | Prevents continuation pages being missed |
| No blank pages in the middle of answers | Blank pages may cause system to skip |
| Structured answers with numbered points | Easier to match against marking scheme |
| Cover page filled carefully before exam starts | Misidentification of scripts is a real risk |
Frequently Asked Questions
Can I use a gel pen for CBSE board exams under OSM?
CBSE does not specify pen type, but gel pens that smear or produce inconsistent ink density are a risk under OSM. A good quality ballpoint pen with dark, consistent ink is the safest choice. Test your pen before the exam.
What happens if my scan is blurred?
You can apply for a scanned copy of your answer sheet after results are declared. If the scan is genuinely blurred and you believe marks were lost as a result, you can apply for re-evaluation. The process is: scanned copy → verification → re-evaluation. Each step has a fee and a deadline.
Should I draw diagrams in pencil and trace over in pen?
No. Draw directly in pen. Pencil lines under pen lines create a double image on the scan. Draw carefully in pen from the start. If you make a mistake, cross it out with a single pen line and redraw.
Does OSM apply to Class 10 as well?
As of 2026-27, OSM applies to CBSE Class 12. Class 10 continues with manual checking. Check cbse.gov.in for any updates before your exam.
How do I know if my answer sheet was scanned correctly?
You can apply for a scanned copy of your answer sheet after results are declared (fee applies). This allows you to see exactly what the examiner saw. If you notice a scanning error, you can escalate through the re-evaluation process.
What is the fee for re-evaluation under OSM?
The fee structure for 2027 will be announced with the results. In 2026, the fee for a scanned copy was approximately ₹500 per subject, and re-evaluation was approximately ₹100 per question. Check cbse.gov.in for the official 2027 fee structure.
Related Guides
- How to Write Answers for On-Screen Marking — 15 Rules So Scanner Doesn't Cost You Marks
- CBSE On-Screen Marking 2027 Explained — What Happens to Your Class 12 Answer Sheet
- CBSE Re-Evaluation After OSM — Scanned Copy, Verification, Re-Evaluation Step by Step 2027
- Step Marking in CBSE 2027 — How Examiners Give Partial Marks in Maths, Physics, Chemistry
- Diagrams and Graphs Under On-Screen Marking — How to Draw So Examiners Can Read Them
- Open Letter to Every Class 12 Student Before Board Exams 2027
Sources
- Indian Express: Mixed-up answer books, unchecked pages, missed step marking in Class 12 CBSE results
- Business Today: CBSE re-evaluation opens, 11 lakh answer scripts requested amid OSM controversy
- NDTV: CBSE defends digital evaluation system amid Class 12 result concerns
- CBSE OSM guidelines — cbse.gov.in
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