Above:  This is a handheld range drum for the 15cm R.K. (Ring Cannon).  The distance from the gun to the target is set on the drum and the rectangular shaped piece on the opposite side, with the leveling vile, elevates.  Then the gun barrel is elevated to the point that the leveling bubble is centered in the glass vile.  The barrel is then at range elevation, so that a projectile fired, with a standard propellant charge, will hit generally at the set range 

Above:  The rectangular piece to the left contains the leveling vile

Above: Nr. 254 is the gun number. Again the leveling vile is on the right of this photograph

Above:  The lever allows the drum to rotate freely

Above:  Looking down on the range drum.  The leveling vile can be seen from this view

Above:  Bottom view of the range drum