Manufactured around 1939 (No. 241xxx ) , this reflex Graflex has remained identical to olders , only the metal plate indicating the speed has changed in appearance and location.
This is a reflex to size 2.25 "X 3.25 " or 6 or 9 cm .
Made of mahogany wood covered with morocco , the body of the camera remains lightweight while showing a real rigidity .
The letters RB mean Revolving Back.  the choice, before shooting between landscape or portrait format is just a matter of a quarter turn of the back.
For this format, several types of back were available: special backs for Graflex rollfilm No 50 , double frame for glass plates or film sheet , magazine backs for 12 or 18 films sheets, adapter backs for film packs, backs forrollfilm 120 ( "22" for size 6 X 6 , "23" for size 6 X 9 ) , back Grafmatic "23" up to 6 film sheets.
Note that these Graflex backs are not compatible with the system Graflock of the Graphic cameras of the  brand .
The lens can be unscrewed and replaced by another one with a focal length slightly longer .

Its operation is as follows , taking as reference the speeds plate  :
1 . Press to the end the trigger 1 rearward makes  the mirror going down, which obstructs the chamber and prevents from any light ingress , only one of the letters I and T ( instant or time ) must be visible , depending on what wants the photographer , the mirror down allows the reflex viewfinder to be used for the framing.
2 . the key 2 can then be rotated in the direction of the arrow to set the size of the curtain opening , visible in the window 3 . In turn , we go from the largest to the smallest aperture , therefore the slowest to the fastest speed (in combination with the spring tension as described hereafter ), the curtain rises to wrap around an axis in the upper part of the camera .
3 . We choose the spring tension from 1 to 6, visible in the window 6 ,using  the rotary wheel 5 . This manipulation, if necessary, is to be done just before the triggering to avoid too long high stress on the spring and the curtain (at rest , always let the tension 1 with button 7) .
4 . Pressing the lever 4 towards the rear, when the trigger 1 is activated , makes the curtain travelling down while keeping the mirror in low position .
5 . pressing the shutter button , located on the other side of the camera, allows shooting . Mirror goes back in upper position followed by the  curtain tracking down a level, depending on the speed selected.
The trickiest part of this device is its curtain : its length of nearly 1.30 meter on this model supports all of  the  mechanical stress, it is nevertheless not uncommon to see it still in good condition after more than half a century of use !