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Indian Journal of Community Medicine

Overhead Projector - A Versatile Teaching Tool

Author(s): Dr. Hemangini K.Shah

Vol. 31, No. 2 (2006-04 - 2006-06)

Here are some tips and rules to make effective presentative using OHP.

  1. Practice giving your presentation using your visual aids to check out how well they project.
  2. Stand off to one side of the overhead projector while you face the audience.
  3. Do not face the "projected" image on the screen. Face your audience.
  4. Cover the transparency when you are done using it.
  5. Place the overhead to your RIGHT if you are right handed and to your LELT if you are left handed.
  6. Place your overhead projector on a table low enough so it does not block you or the screen.
  7. Place your screen on a diagonal instead of directly behind you.
  8. Keep your slides in order.
  9. Be Enthusiastic and Confident.
  10. Do not touch the stand of the screen unnecessarily.
  11. Do not talk unless you have eye contact.
  12. Do not read a visual aid to the audience.
  13. Tape the power chord to the floor-to protect you or someone else from tripping.
  14. Store your overhead transparencies in a sturdy box or container.
  15. Do not touch the screen.
  16. Pointing on the slide: A hexagonal pencil, a slide with an arrow drawn on it and plastic or card board arrows all make good pointers.
  17. Remember to allow plenty of time for a projection to be read and understood.
  18. Do not place the transparencies in front of the OHP fan.
  19. Place the new transparency over the old and quickly slide the old transparency from below.
  20. Overlay Technique: Three or Four transparencies can be used as overlays on the original transparency. This technique is a very effective method of "Building Up" or Dissecting Down" a complex diagram.
  21. Silhouetting Effect: Opaque Objects laid on the stage of the projector are silhouetted. For instance, a Smith-Peterson nail can be placed over a rough sketch of the fractured femoral neck when the fixation of these fractures is being discussed.

Preparation of Material for an OHP

Acetate (Plastic) sheets are available in different thickness. The Thicker the sheet, the greater is its durability, but so is its cost. Water inedible ink or permanent markers are better for use. Alcohol / Methylated spirit can be used to erase them. The sheets may also be mounted on card board frames so that the transparency does not fly off.

  1. Do not crowd the transparency. Follow the rule of 7 i.e. Not more than seven words in one line and not more than seven lines on one Transparency.
  2. For titles limit the use to Five words or less.
  3. Do not use faded pens for writing the text. It decreases clarity.
  4. Don't Use Red colour pen sparingly for headings or underlining or highlighting. The best colors to write on a transparency are BLACK and BLUE.
  5. Don't put your whole speech on transparencies, just key points and ideas.

Remember: You are the focal. Point of the presentation use the aid only to support your talk and not to deliver it.

Advatages of an OHP

  1. It does not require darkening of the roam (unlike a slide projector) thereby allowing audience interaction.
  2. It makes it possible to present while facing the audience.
  3. Image can be projected high up to enable all to see clearly.
  4. Relatively easy to use.
  5. Provides flexibility to skip slides.
  6. Since transparencies are pre - prepared, the speaker can concentrate on the talk and save time.
  7. Easy to project complicated diagrams as they can be traced/ eroxed and hence make up for lack in drawing skills.
  8. Since matter can be typed and eroxed, or external help used, one need not depend on ones own handwriting (unlike a chalkboard where bail handwriting is a handicap).

Disadvantages of the OHP

  1. It is totally dependent on electricity.
  2. As compared to a slide projector, it is a little bulky. Hence difficult to shift.
  3. Needs accessories like a screen, a stand, an extension board, sockets etc.
  4. Since transparencies can be reused, lethargy may set in. Same old transparencies may be used for years.
  5. Can serve as a distraction.


  1. Kroeger L" Choose the visual -Aids Medium carefully". The complete Idiots guide to successful business presentation Prentice Hall of Fame, New Delhi, 1998, 129-135.
  2. Kroeger L." Using Visual Aids & Machinery " The complete Idiot's guide to successful business presentation, Prentice Hall of Fame, New Delhi, 1998, 239-247.
  3. Rumar S" Teaching learning Medie: The means to an end", Medical Education Principles & Practice, 2nd edition, 64-71.
  4. Saha T.K. & Bhatnagar R, " Audio-Visual AIDS " workshop on Lecture-A tool for Medical Teaching, Dept. of Medical Education, AFMC Pune March 2000, 25-26.
  5. Yeolekar M, "Teaching Learning Methodolagies", The Art of Teaching Medical Students, 1998, 8 -12.

Dr. Hemangini K.Shah,
Lecturer cum Epidemiologist
Department of SPM, Goa Medical College
Received: 23.09.2004

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