Tekpower Tachometer features the most popular one on the market.
Specifications:
It is a large display with 5 digits large LCD 15mm (0.6");
Range: 0.5 to 19,999 RPM;
Surface speed: 0.05 to 1,999.9 (m/ Min);
Resolution:0.1 RPM (0.5 to 999.9RPM); 1.0 RPM >1000 RPM
Surface speed: 0.01m/min (0.05 to 99.99m/min); 0.1 m/ Min (over 100m/min);
Accuracy: +- 0.05 % + 1 digits;
Range selection: Auto ranging; Sampling Time: 0.5 seconds (over 120RPM);
Power: 4 AA batteries (not included).
AC adapter, Carrying case, Cone adapter, Funnel adapter,
Surface speed test wheel and operation manual book are included.

• Measures wheel/shaft RPM or linear surface speed
• Memory recalls the Min and Max of the readings.
• High resolotion and accuracy.
• 5-digit large LCD display
• 90 days money back guarantee and 1 year limited warranty

Measures wheel/shaft RPM or linear surface speedTekpower