Obedience to Authority: An Experimental View (Perennial Classics)

ADIBO Tennis Ball Machine, Internal Oscillation, Authentic Programming, Dual Motors with Topspin & Backspin, 160+ Balls, 6-Hour Non-Stop Runtime, Stable Voltage Contro (T500 PRO)

PUSUN Tennis Ball Machine, Portable PT-Mini Pro Tennis Ball Serving Launching Machine for Practice and Training, Support App and Remote Adjust Speed&Angle, Hold 65+Balls at Once, Easy to Use

Furlihong 3819BH Portable Tennis Ball Machine – 5 Adjustable Angles, 2 Power Levels, 4 Serve Intervals, Up to 30 MPH, for All Skill Levels Training

PUSUN｜PT-Smart Pro Internal Oscillation Tennis Ball Machine: App with 12 Built-in Training Modes, 28-Pt Custom Drills,75MPH, 5H,32.6lb Portable for Tennis & Padel,Training, Practice,Beginners to Pros

PONGBOT Tennis Ball Machine, APP and Remote Control, Custom Drills, 150 Ball Capacity, Max 80mph,8+ Hours of Endurance, Dual Motor for Topspin and Backspin, PACE S PRO

PUSUN PT-MINI Pro Tennis Ball Machine: Automatic Serve with Adjustable Speed and Angle. Durable Build, high Capacity, Remote-Controlled. Premium Training Tool for Players of All Levels. (White)

PUSUN PT-Smart Tennis Ball Machine: App Control,12 Drills,6-Level Spin,28-Pt,14 Padel Modes,75 MPH,32.6 lbs,100+ Ball, 5H Battery, Portable, for Fitness,Coaches,Solo Practice,Pros,School (Black)

Furlihong 3807BH Tennis Ball Machine with Triangular Base, Adjustable Speeds, Oscillating Left&Right, Up&Down Swing Launch Port, for All Levels Training