Army Bacteriologicalhad the higher profile, all other Bacteriologicals being an inch shorter. Also note the rack and pinion focusing to the substage on the earlier model, wheresas all later models except the Army version, had the coarse vertical screw focus to the substage, controlled from the opposite side. The earlier model has a plain brass drawtube and tailpiece supporting the mirror assembly whereas on the later model both the drawtube and tailpiece are nickel-plated. Note also the earlier model has an articulated mirror support, while in the later shorter model, there is only a straight connection between the mirror gimbal and the collar on the tailpiece.