The Smart Stir is a magnetic stirring device that makes mixing your testing solutions totally painless. Portable with single click operation and LED illuminated for better distinction of color endpoints. Automatic shutoff after 4 minutes for improved battery life. Optional LED lights illuminate your tube, making color changes more visible. Fits all industry standard pool testing and mixing tubes (25-32mm diameter), and is 100% compatible with all TFTestkits tubes, kits and tests. Includes a heavy duty 40mL mixing cylinder embossed at 5mm increments, magnetic stir bar, 4 AA batteries, and instruction slip.