Such screens are mounted on a rotatable member having an exteriorly accessible handle whereby the rotatable member and screens thereon can be rotated at least ninety degrees and preferably one hundred eightly degrees so that the force of the fluid under pressure cleans off the screen and enables...
an overhead projector. The writing-film is used by cranking it from the spool, across the stage of an overhead projector, onto another overhead projector spool. The teacher writes on the film as he gives his lecture, and the writing is projected onto a screen. Gradually, the entire roll...