Fig. 3 A classroom divisible into two seminar room».
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structions, slope of the floor and height of the speaker's platform, viewing distance, and the extreme vertical and horizontal viewing angles. It is clear that a good lecture room will not have columns or supports so placed as to block the front screen and chaikboord from any seat in the roam. However, when a large demonstration table stands on a platform between the chalkboard and the audience, the lower 12 to 18 inches of the board often cannot be seen by people in the first few rows. In this case, vertically sliding chalkboards are needed so that the writing may be raised to a level where it con be seen by all. A sloping floor in a lecture room will generally add somewhat to the cost of construction, but in many instances it will be worth the extra cost in providing good visibility for all. The object of a sloping floor is to make it easier for a person to see over or around the heads of those in front of him and to give the impression of o smaller room. If the seats in successive rows are staggered so that the line of sight from one seat to the lecturer goes directly between the centers of two seats in the next row, the rise required per row may be reduced by half. Closely interdependent are the slope of the Floor and the height of the speaker's platform. The use of a raised platform for the teacher hos advantages in increased visibility in any room seating more than about 40 persons, provided that the table or other furniture on the plotform does not block the chalkboard for those in the front rows. [A possible plan is shown in Fig. 5.]
Studies of distances and angles for satisfactory viewing indicate that seats should be placed at a distance from a screen not less than twice nor more than six times the width of the screen image to be viewed and thot the distance from a person to the chalkboard should not exceed 400 times the siie of the smallest letter or digii being written. Thus, if the back row of students is 64 feet away, the lecturer should make his letters and digits at least two inches high. Similar studies indicate that the angle of elevation from the eye to the upper part of an object on the screen or chalkboard should not exceed 30 degrees (see Fig. 4). If lecture rooms are built in a fan shape instead of a rectangular shape, the minimum angle between line of sight and the blackboard should be at least 30 degrees and preferably more than 45 degrees. These (imitations of viewing distance and angle impose restrictions on the placement of seats for adequate viewing.
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