Readable Letter Size and Visibility for Overhead Projection Transparencies

SARAH ADAMS

ROBERT ROSEMIER

PHILLIP SLEEMAN

INTRODUCTION Since x9x9, about twenty-five hundred research studies have investigated the instructional use of the new media in communi- cations. Several of these studies are related to the more elaborate and expensive media such as motion picture projectors, televi- sion, teaching machines, and computers. One of the newest mediums of communication is through the use of the overhead projector. It has inspired the imagination of many educators since it may be used by the teacher in the front of a normally lighted classroom. This technique will also allow the teacher the advantage of eye-to-eye contact, more efficient posing of the lesson, and thus more effective classroom control over the learn- ing environment. These facts are significant since most other mediums for presentation neglect these important teaching- learning techniques.

A survey of the literature concerning both the use of this new medium and, most important, the proper letter size for effective

Sarah Adams is audiovisual coordinator for the Spring Valley, New York, school system. Robert Rosemier is associate professor of education, Northern Illinois University, DeKalb. Phillip Sleeman is director of the Boston Univer- sity Krasker Memorial Film Library, Boston, Massachusetts.

4x2

READABLE LETTER SIZE : 4 1 3

viewing via the medium has indicated a serious lack of research in the area. While lettering standards have been established and reported for motion pictures, filmstrips, and television, these, too--even though they generally apply to the overhead pro- jector technique--seem to lack statistical foundation. This ab- sence is evidenced by the vagueness of the information reported in the studies. Due to the present national interest in this medium (approximately zoo,ooo projectors are now in use in the United States, with a predicted total figure of 5oo,ooo during the next three-year span), the establishment of a statistically sound lettering size is felt to be absolutely necessary for proper view- ing in an effective teaching-learning situation. Regardless of whether one or a hundred projectuals are used, one question still confronts the teacher preparing lettered projectuals: How large is large enough to read? The purpose of this research study, therefore, was to investigate the readability of various sizes of type which are equivalent in height to the elite type, the pica type, primary type, and the commercially recommended size of one-fourth inch. The investigation studied these sizes of print at varying distances from the screen for various grade levels.

THE MATZRIALS Using the ~o letters of the Snellen Eye Chart and a table of ran- dom numbers, z 5 sets of four letter combinations were formed. The z 5 sets were subdivided into five categories, and one of five letter sizes was assigned to each category. Thus, five sets of four letters each were derived and assigned to the size 3/32 inch (elite type size); five sets to 4/32 inch (pica type size); five sets to 6/3z inch (primer type size); five more sets to 6/3z inch, but employing bulletin type (sans-serif); and the remaining five sets to 8/32 inch (commercially recommended size). An electric type- writer equipped with elite type provided original copy from which the letters were photographically enlarged to the other sizes, excepting, of course, the bulletin type which was directly produced from an electric bulletin typewriter. The materials were then duplicated onto clear-base Diazo film, which constituted the projectuals used in the study.

Each projectual contained one set from each size category, or a total of five different transparencies (each including five size categories, and each size category consisting of four letters). In order to assure measurement of normal perceptual ability rather than "extruded" ability developed through sequential con- ditioning of discriminatory faculties, the order in which these

AV COMMUNICATION REVIEW : 4Z4

size groups would be presented on a projectual was specifically manipulated. This manipulated control caused middle sizes to appear at the beginning and end of a presentation, the largest size in the middle, and the smaller two sizes acting to separate the others. The order so determined was as follows: (z) bulletin type and size 6/32" , (2) elite type and size 3/32'', (3) elite type enlarged to 8/32", (4) elite type enlarged to 4/32'' , (5) elite type enlarged to 6/32". The sequence and letter assignment for one of the five projectuals are shown in Figure x. The four letters in each size category had a mask covering them which could be flipped back when they were to be projected.

FIGURE I

Letter Assignment and Sequence of

Sizes for One Projectual {Not

the Projected Image Size)

D F E 0 PTEO

F 0 Z C FLCT

PTE 0

FIGURE 2

Projected Image Size of Letters at a Given Distance

of Seven Feet

F

Sequence of Sizes Projected Image Size 8" D F E 0 I~-

P T E 0 8'___~' 32

20 tt 0 Z C F L C T 28__~"

32

8" PT E 0 ~

THE SUBJECTS The experimental subjects consisted of unselected children in grades one through six (exclusive of grade four, which was used for a field trial of the materials and procedures) in the Mark's Meadow Laboratory School of the School of Education at the University of Massachusetts. These subjects numbered 22 chil-

READABLE LETTER SIZE : 4 1 5

THE PROCEDURE

dren in grade one, 24 in grade two, 22 in grade three, x 9 in grade five, zo in grade six--a total of zo 7 subjects. Each size category on a given projectual was presented as an in- tact group for a period of eight seconds. The children were asked to list each letter that they saw on a specially prepared response form. They were allowed to make their response during the eight- second exposure period or continue into a five-second "blank" period following the presentation of each size category. The next size category was then presented, following the same procedure, and so on until all five categories had been presented on that pro- jectual. The subjects in a given row at a given distance from the screen were then asked to move to a different prearranged row in the experimental room. At this distance, a new projectual was shown by the same procedure as the first, and again showing sets of all five sizes. The children then moved to a third row, and so on until they had responded at each distance of 20 feet, 25 feet, 30 feet, 35 feet, and 4o feet from the screen.

The experimental room was equipped with blackout curtains, a 7 ~ X 7 ~ anti-Keystoned matte screen, a Besseler overhead projector (with a 5oo-watt lamp), and chairs and tables arranged into five rows (with the chairs at the above-mentioned distances from the screen). To assure uniformity of directions and for tim- ing the projectuals, prerecorded statements and artificially in- duced "clicks" were played for each group of subjects with the tape recorder. The same degree of artificial, incandescent light- ing was used with each grade group. A score of one was assign- ed to each letter properly reproduced on the answer form, thus allowing a possible maximum score of zoo per subject (four letters per size category X five size categories X five distances). The mean scores of each letter size at each distance for grade five, which is typical of the other grades, are presented in Table I.

TABLE I Distance (in Feet) Mean Scores for Letter Size 20 25 30 35 40

Letter Sizes at 1 3.37 2.95 3.47 2.95 3.26 Each Distance

Attained by 2 2.74 2.47 1.89 1.37 1.11 Grade Five 3 3.79 4.00 3.79 3.84 3.47

Subjects 4 3.79 2.84 3.00 2.63 2.63 5 3.89 3.95 3.53 3.74 3.37

THE RESULTS Analysis of variance procedures was used to analyze this treat- ment-by-treatment-by-subject experimental design. F-statistics

AV COMMUNICATION REVIEW : 4Z6

TABLE 2

Inequalities Show-

were computed for each grade to analyze for main effects of dis- tance and letter size, and for interaction of the two. For testing the interaction effect at each grade level, the denominator of the F-ratio (the error term) was the triple-interaction term (distance by size by subject) for that grade. The interaction was found to be significant in grades two (p < .o~), five (p < .o5), and six (t, < .02).

Because of this interaction, further analyses were performed at these grade levels (two, five, and six) to determine which letter size(s) showed a distance effect. In each of these grades, letter sizes two and four (the smaller sizes) differed significantly at the various distances, while the other letter sizes tended to re- main equally visible over all distances. Relatively imperceptible differences between letter sizes were noticeable at closer dis- tances, but these differences became quite large at further dis- tances due to significant drops by letter sizes two and four. In grade one, differences among letter sizes remained relatively constant at each distance. At grade three, all letter sizes exhibited relatively the same distance effect as was noticed in the vertical S pattern of the letter size distance plots. In this grade, the dis- tance of 25 feet showed significantly higher results than did the distances of 35 and 4o feet. At all grade levels, letter sizes five and three were significantly better (p > .oz) than letters of sizes two and four. At all grade levels except grade one, size four was significantly better than size two. Only at grade two was size five significantly better than size three. At grades one, two, and three, there was no significant difference noted between sizes one and three, and no significant differences at grades five and six between sizes one and four. Using a system of inequalities, the significant size differences are shown in Table z.

Grade Size

ing Significant Differences

Among Letter Sizes

1 5 , 3 > 3 , 1 > 4 , 2 2 5 > 1 , 3 > 4 > 2 3 5 , 1 , 3 > 4 > 2 5 3 , 5 > 1 , 4 > 2 6 3 , 5 > 1 , 4 > 2

CONCLUSIONS The results of this investigation would indicate that the smaller- size letters (elite and pica) should be avoided in the preparation of projectuals---certainly for viewing distances beyond zo feet.

R E A D A B L E L E T T E R S I Z E . 457

Further investigation could be, and probably should be, con- ducted at distances less than 2o feet to determine if anything significant would be lost by employing these smaller sizes for the closer distances. The smaller sizes are likely to be sufficient for distances of 2o feet or less.

At further distances where larger-size letters are needed, probably the most feasible approach would be to use the primer type 1 available in many schools. It is quite interesting to note that four of the five grades found the 6/32 inch primer size type with serif to be more readable than the 6/3z inch bulletin type without serif. Many casual observers would erroneously suggest that the simple bulletin type would be less confusing and thus more readable. Needless to say, this observation may be a phe- nomenon of the sample and might not similarly be observed in a replication of the study.

The largest size, that which was commercially recommended (8/32 inch), did not appear necessary; the 6/3z inch elite type (primer size) was statistically equal to the larger size in four of the five grades, while in the remaining grade, the primer size actually surpassed the commercially recommended size. The three largest sizes showed approximately equal, minimal change from closer to further viewing distances. In future studies, initial measures should be made of the visual acuity of the subjects to control this possible source of variation. Additional attention also needs to be paid to the characteristics of specific letters which make them more difficult to read, regardless of size.

1 This primer type process may be substantially improved by following the recommendations for lettering as specified in PhiUip J. Sleeman's articles, "How's Your Lettering?" (Massachusetts Audio Visual Newsletter, Vol. 7, No. 5, June ~965) and "Lettering Process Simplifies Overhead Projectual Problems" (Reproduction Review, Vol. z4, No. 6, June 2964).