shown by arc 23 it is biased upwardly by a bias spring 24 in compression between the under side of the platform and the arm the function of the platform is to support and position a jacket 25 on the upper surface 22 location pins 26 rise from surface 22 to fit in locator holes 27 in the jacket this positions the jacket relative to the platform and keeps it from moving around jacket 25 has a top sheet 28 and a bottom sheet 29 in order to form channels 30 the sheets and inserts are bonded to spacer ribs 31 which form side walls of respective channels the sheets are made of transparent material so that an image on a microfilm frame between them can be projected entry slots 34 are formed in the top sheet one for each channel the slots and the dimensions of width of the channels are slightly larger than the width of the microfilm material the height of the channel is bit less than the thickness of the microfilm material the jacket has an entry edge 35 from which the entry slot is axially spaced this leaves a flexible portion 36 which can be deflected downwardly over edge 37 of the platform there is no intended backing for the under side of portion 36 portion 36 is springly flexible and as will be.