When using an OMR (Optical Mark Recognition) sheet, each mark must be clear and fully readable by a scanner. Mistakes such as smudges, incomplete erasure, or damaged sheet material can lead to unreadable bubbles, mis-reads or even rejection of the sheet. The process of erasing becomes particularly delicate because the sheet has special index points and bubble areas intended for machine reading. As the Addmen Group blog explains: “Using a pen eraser is likely to thin and damage the OMR sheet… When you are using a pen… there is no way you can erase the marks.”
When the exam body allows or specifies pencil (e.g., HB pencil) for filling bubbles, you can erase an incorrect bubble. However, you must use a soft, good-quality eraser so that:
All the pencil mark is removed completely — leaving no faint residual trace that could be read as a stray mark.
No smudging remains around the bubble or elsewhere on the sheet — smudges may cause the software to detect double-mark or invalid responses.
After erasing, blow away all rubber-dust from the sheet so that no small particles interfere with scanning.
Make sure the bubble area remains intact, not torn or weakened from erasure pressure.
When the instructions mandate a black/blue ballpoint pen (which many modern OMR exams do) then erasure is essentially not possible. According to Addmen Group:
“Never attempt to erase pen marks, as it may create holes or damage the sheet, rendering it unfit for automatic evaluation.”
Using whitener (correction fluid) is strongly discouraged in most cases because it may:
leave opaque white patches that might confuse the scanner
chip off or cause impressions on adjacent sheets
damage the ability of the sheet to be processed automatically.
Best practice: If using pen, avoid marking until you are sure of your answer. If a mistake is made, speak to the invigilator/exam body for instructions.
Use soft, good quality eraser (if pencil filling allowed) that removes the mark cleanly and does not abrade the sheet.
Remove all rubber dust after erasing.
Ensure no smudges or stray marks near bubbles or in answer blocks.
Read the instructions printed on the sheet carefully (some sheets allow pencil, some require pen; some may permit correction fluid, others not).
If a correction is needed, after erasing correctly, fill the correct bubble fully (with pencil or pen as per instructions).
Make sure no folds, creases, staple marks or damage exists — these can interfere with the scanning process and erasure may worsen damage.
Don’t attempt to erase pen marks — you risk damaging the sheet or leaving traces that the scanning software might detect as marks.
Don’t use correction fluids/whitener unless explicitly permitted and dried properly. They may chip off or cause scanning issues.
Don’t leave faint or partial erased marks — even very light pencil remains might be detected by OMR software as stray marks.
Don’t over-rub or press hard while erasing, as that may damage the paper surface, create dents or thin spots.
Don’t ignore instructions on the sheet – if the sheet says “Pen only” then erasing is not intended.
The scanning software reads darkness and contrast of filled bubbles — any faint marks, smudges or damaged paper may cause misread, duplicate detection or invalidation of a response.
A sheet with erasure damage or residual mark may be flagged for manual review, increasing cost/time for exam bodies.
Inaccurate erasure may lead to data mis-capture — e.g., the system might detect two marks in one bubble, or an erased mark as attempted answer.
For large scale examinations, even small percentages of unreadable sheets can lead to significant delays or erroneous results — so following correct guidelines improves reliability and throughput.
For Candidates: If you are allowed pencil, work lightly, be confident before marking, and erase cleanly if you change your mind. If pen is required, double-check your answer before marking. But don’t panic if you make a mistake — inform invigilator.
For Administrators/Invigilators: Provide clear instructions on the sheet regarding filling and erasing. Ensure exam-center staff remind candidates about erasure risks. Provide high quality erasers, avoid allowing correction fluid unless permitted, and supervise carefully.
For Printing/Scanning Teams: Ensure sheets are printed with correct index points, sturdy paper stock, and that scanning parameters are set accounting for possible erasures (especially in pencil-filled cases) so residual marks don’t cause false reads.
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