Readable letter size and visibility for overhead projection transparencies

Conclusions

The results of this investigation would indicate that the smallersize letters (elite and pica) should be avoided in the preparation of projectuals—certainly for viewing distances beyond 20 feet. Further investigation could be, and probably should be, conducted at distances less than 20 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 20 feet or less.

At further distances where larger-size letters are needed, probably the most feasible approach would be to use the primer type¹available 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 6/32 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 phenomenon 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 6/32 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.