This digital tachometer is used to measure the motor propeller RPM remotely using infrared. It's  also a great tool when you try to figure out which propeller works best with your motor configuration.

Measures rpm of propeller or fan up to 9 blades and record maximum, minimum and final reading in memory. 

Specifications

• Display:                                    5-digit LCD, height of digit: 18mm
• Measuring range:                     2.5-99999 RPM
• Resolution:                               0.1RPM（2.5～999.9RPM), 1RPM (over 1000RPM)
• Accuracy:                                 ±（0.05%+1character）
• Responding time:                     0.5 second（over 120RPM）
• Measuring range choise:         Automatic
• Effective distance：                 50mm - 500mm
• MAX current：                         40mA
• Data record：                          automatically record Max.,Min. & final measurement results
• Battery:                                     4.5V (3 cell) AAA battery
• Dimension:                               184X76X30mm