Godox Speedlite TT600 2.4G Flash with GP Rechargeable BatteriesKey Features Guide Number: 60 (ISO 100 105mm), 22 steps of power output (1 1~ 128) In the 2. 4G wireless transmission mode, when used as a master unit, TT600 can set its group as M A B C D E; when used as a slave unit, TT600 can set its group as A B C D E; there are 1~32 channels to be chosen Specifications: Model: TT600 Guide Number: (ISO 100 105mm), 22 steps of power output(1 1 1 128) Vertical Rotation Angle: 7~90 Horizontal Rotation Angle: 0~360