In preparing a talk for presentation at any conference, one should bear in mind that talking to an audience is often a very inefficient means of communication. Roughly half of what we hear is lost immediately, another quarter is lost within a few hours, and almost nothing of the detail is retained after 24 hours unless the information is directly applicable to ones own research. Although, talks are often used to give information, this is the least effective use for oral communication. It is far more useful as a means of opening on-going research for discussion and constructive criticism, for stimulating interest in a topic among colleagues and students, and for generally enhancing communication among phycologists with common interests.

Good oral communication has good writing as its basis, for both writing and talking involve organisation, logic and clarity of thought. Only the medium differs, but the difference in the medium has major implications in terms of content and style of presentation. Most notably, the amount of detail that can be presented orally is far less than the amount of detail that can be presented in written form. Therefore, text and illustrations that are suitable for use in a written publication are almost never fully suitable for use in an oral presentation. If no other message comes through from this document, let it be this one!

A good talk has a number of primary features. It must be pitched at the level of those persons likely to be in the audience. Since most of the delegates at a conference will not be familiar with the details of each research area within a broad field, it is crucial to provide a clear and simple introduction to your topic. It is also important to remember that the simpler you can make your topic seem, the more people will understand it, and the more people will come to regard you with respect. It is also important to present the material clearly, in an organised manner. All of these aspects of a good presentation can be facilitated through the preparation of good visual aids.

There are essentially two types of visual aids used at International Phycological Congresses: overhead transparencies, and 35 mm slides. Each has advantages and disadvantages, although 35 mm slides are generally better than overhead transparencies in most circumstances. While it is possible to mix overhead transparencies and slides in a single talk, it is usually much more efficient and effective to use one or the other, but not both.

Overhead transparencies have the advantage of being relatively quick, easy and cheap to produce, as well as being flexible and amenable to last minute changes. Their main advantage, however, is that they can be used in a lighted room. Their main disadvantages are that they cannot show photographs very well, and they tend to look sloppy when prepared by hand. They can also be confusing for inexperienced speakers, and the apparatus is obtrusive and often gets in the way. Overheads should really only be used:

• to present the results of a discussion exercise during a workshop;
• if you cannot afford to make 35 mm slides, or do not have the facilities to do so;
• you know that you will be talking in a lighted room.

If you choose to use overheads, use large fonts, and try to make your transparencies using a computer package and a laser printer. If you do not have access to a printer that can print on transparencies, print on paper, and use a photocopier to make the transparencies. Try to avoid hand-written overhead transparencies. As noted above, do not photocopy printed or typed tables, because they are inappropriate anyway in a talk, and their small fonts are illegible when projected. You should never, under any circumstances, use any overhead for which you have to say, "I know you can't read this but..." The points below concerning what makes a good slide also apply to overhead transparencies.

Slides have the advantage that they can show pictures and colour-coded graphs easily, the apparatus for showing them is unobtrusive, and they are accepted as the standard international format for oral conference presentations. Colour can also be used to great effect to highlight ideas or concepts, and if a difficult concept is being presented, a series of slides of increasing complexity can build the concept through adding ideas one at a time.

The main disadvantage of slides is that they require a darkened room in which to project effectively, but most conferences cater for this nowadays. Slides can also be expensive to produce (as much as US$12 each if commercially printed from computer packages such as Harvard Graphics® or Corel Draw®), and last minute changes are impossible. They also need to be made well in advance in case problems are encountered.

Below are some suggestions for producing a good, professional presentation using 35mm slides. Included are suggestions that pertain to preparation, the slides themselves, as well as to the presentation. Please study them when you are preparing your presentation, and check your work against each suggestion. If any suggestions are not complied with, please consider what you may need to do to correct the situation.

1. Provide a simple and clear introductory overview pitched at least expert persons in your audience.
2. Title slides are not usually necessary, since you will usually be introduced by the chairperson, who will read your title from the conference programme.
3. Provide a visual aid for every point you wish to make.
4. State your questions or hypotheses clearly in point form on one or more slides. Make sure they are legible (see below).
5. If you wish to provide a simple and tastefully prepared slide summarising your main points at the end of your talk, don't label it Conclusions. Use only key words in the summary or, better yet, try to use a flow diagram or mind map, and make sure the text is legible (see below). Leave yourself something to say after you switch on the lights, to ease your audience into the question period.
6. The message on any one slide should be limited to one single idea, concept, comparison or aspect.
7. Slides should contain absolutely no noise, visual clutter or redundancy.
8. Show a slide or two of your specimens if you work with living material, but don't overdo it.
9. Avoid making slides from material designed for a printed medium. Text, data tables and graphs in a form used for publication or in a thesis are rarely suitable for projection during a talk.
10. Avoid showing a slide with 'classic' outlines that say nothing (e.g. Introduction, Materials & Methods, etc.).
11. If you have no slide to back up a particular point, do not leave the previous or next slide up when you are talking, as you will confuse the audience. Rather use a blank slide or, better still, have a slide with keywords on it.
12. Never present raw data in a talk.
13. Never present tables with more than 4-5 numbers.
14. Never present tables or graphs where trends are not obvious at a glance. Extract significant data and highlight it. Be creative in doing this.
15. Use colour to enhance your presentation, but don't overdo it, and make sure that the colour combinations you choose project well together.
16. Don't present low quality photographs unless they are of the Loch Ness monster or a Sasquatch grazing on algae.
17. If you are presenting a micrograph slide, do not use the style of a journal plate for layout. This is designed for the printed medium, and should not be projected to an audience under any circumstances. Rather, take the trouble to pick out the illustration that you want to show, and photograph it separately, or scan it into a bitmap image, and annotate it on your computer screen.
18. Micrographs, photographs of structures, and cell or tissue drawings should be adequately labelled.
19. Micrographs and cell drawings should not be labelled with the shorthand notation used in a journal plate. Give labels in full wherever possible as most of the audience will probably not have any idea for what an "a" on a micrograph stands. If you cannot give labels in full, leave them off and explain them using a pointer, or refer to labels in the photograph margin.
20. If the same information is needed more than once during a talk, use multiple copies of the same slide so that you do not need to back-track through slides that have already been shown.
21. Do not use all CAPITAL LETTERS ON A SLIDE. They are too difficult to read quickly, and can be distracting.
22. Wherever possible, try to avoid having to refer to a written outline. Let your visual aids be your prompts, but do not talk to the screen. Glance at it, and then talk to your audience.
23. Try not to read from a prepared document. A better sleeping pill has not been invented.
24. Do not present something you don't understand or are not sure about. You will be hammered!
25. Abbreviate sentences and other long text so that the slide contains only essential key words that are tastefully arranged on the slide.
26. Instead of presenting a single complex slide, present a series of simple slides which progressively add information.
27. Slides should convey a message that is direct, simple, brief, clear and to the point.
28. The slide should be designed to appear on the screen for a sufficiently long time to inform, and not long enough to become boring. Generally slides should be on for not less than 10 seconds and not more than 30 seconds. If your slide must be up longer than this, consider making it into a series of slides of increasing complexity as noted above.
29. All slides on the screen should be relevant to what is being said.
30. Use photographs if they help you to make a point, but don't overdo it.
31. Show a flow chart if a logical argument is being presented, and build it up step-by-step.
32. Use an organisation chart (such as those shown earlier in this document) to help you and the audience get oriented.
33. Use humour to keep your audience alert, but don't overdo it.
34. Keep slides to a horizontal (landscape) format when ever possible.
35. If you are making slides from a computer screen, or by hand, print onto an A4 sheet, and note the following:
    Safe area: 225 mm X 150 mm
    Letter height: 6 mm, 5 mm, 0.4 mm
    Line thickness: 1.5 mm, 0.8 mm, 0.4 mm
36. Check your slides for legibility as soon as you get them. If any are not legible, they should be redone. Hold the slide at 50 cm from your eye, against a light source such as a window, and if you cannot read the lettering, then neither will the audience when the slide is projected.
37. Mount all slides uniformly to facilitate focus and smooth operation of the projector. If you have slides with different mounts, remove the mounts from the odd ones and replace them with the common mount. Never use thick plastic or glass mounts, and never include slides with damaged mounts.
38. Mark each slide according to international convention. A dot at the bottom left of the mount as one holds the slide up and looks at it in the correct orientation. This dot usually goes top right under the ball of the thumb as the slide goes into the tray for most projectors.
39. Number your slides in the required sequence by writing on the front of the mount, and write your name on the mount as well.
40. Supervise the loading of the magazine at the conference venue.
41. When giving your talk, do not mumble. Speak loudly, clearly and firmly. If you absolutely cannot project your voice, consider offering a poster instead of a talk.
42. Timing is crucial in giving a conference presentation. You must rehearse your talk before you leave home, and make sure that it fits within the allotted time. If it is too long in rehearsal, shorten it. Do not allow it to go over into the question period, as the questions may be more important than the talk since they may generate further contact with colleagues.
43. Critical to the timing is the number of slides that you have in your presentation. There are no hard-and-fast rules about the number of slides, but generally, one slide for every 30 seconds of talking is comfortable as long as your slides are kept simple. Thus, a fifteen minute talk would have about 30 slides, plus or minus 10 slides depending on their complexity. Forty-five slide would be the absolute maximum for a 15 minute presentation, and in most cases would be far too many.
44. Students should remember that at a conference, the impression people gain of your performance can affect your career as a scientist.