Check the listing for details. 4 Digital Tachometer RPM Speed Meter+Bracket & Magnet Proximity Switch Sensor RD. Condition: New. Listed at 13.88 USD. Feature: Working power supply: DC8-24V, 40mA Display mode: 0.56"LED,4 Digital measurement range: 10-9999RPM Measuring Accuracy: ±0.1, reading ±1 word Display refresh rate: >3 times/sec Overrange display: the first one shows "1" or "-1", and the latter three do not show Physical dimension: 79x43x26mm Precautions: 1. Connect the plug correctly according to the wiring diagram 2. Should avoid strong electromagnetic interference and it is better to use shielded wire or double stranded wire for measuring conductors 3. The counting signal of the counter and the switch of the zero clearing signal input or the circuit shall be as close as possible to the terminal of the counter to make the signal line as short as possible 4. Avoid with other such as: high voltage wires or .