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 photographs are carefully dated and filed for reference in case there should be any dispute later regarding the progress of the work and payment therefor. If a large card giving the date of the work is placed in front of the camera so that the date is photographed directly into the picture, the date is somewhat more easily proved than it would be otherwise. Putting the date card in front of the camera with the date upon the card gives a chance for any passer-by to check the honesty of the date on the picture, much as the "amount purchased" card at the front of a cash register checks the honesty of the clerk.

Progress photographs like those described above are particularly effective for use in advertising. A series of three or four pictures placed one below another, with the dates carefully stated on each, give the best possible demonstration of the rapidity with which construction work has been completed by the advertiser. A broad use for these progress photographs is found in the preparation of reports, catalogues, magazine advertising, etc. Thus a manufacturing plant, for instance, can be pictured in a series of photographs taken some years apart showing buildings which have been added to provide for increase in the business. In the case of machinery, a series of photographs taken in different years are of value to show the increase in the size of the machines built or the successive improvements made in the design.

Moving-picture machines have opened up a whole field of possibilities in the rapid conveying of accurate information. Many companies are now using moving-picture films to show the technical operations involved in making up their manufactured product, or to show views in different parts of a factory. Moving-picture cameras have been used also in a very striking way by Mr. Frank B. Gilbreth as an adjunct to methods of time and motion study. By placing in the camera field with the worker a clock with a large dial and a sweeping second hand, an automatic and permanent record may be secured both of the worker's movements and the corresponding elapsed time. The statistics thus graphically recorded are immeasurably more accurate and more conclusive than any that could be secured in any other way. Possibilities for the use of moving-picture machines in educational work in schools are only beginning to be grasped by a few of the world leaders in thought. When the moving-picture machine becomes a feature of every school room the results will be astounding.