RL-HM011F Digital Tachometer is pretty accurate. I highly recommend this. I tested mine on my 3.5 HP Tecumseh engine, and compared it to the 670156 Vibration Tachometer recommended by Tecumseh in their engine service manuals. The results were nearly identical. I high recommend this Tachometer for it's accuracy, it's fair price, and this seller's quick shipping. Enclosed are pictures show the Tachometer I received tested on my old 1982 Montgomery Wards snowblower with a Tecumseh 3.5HP engine. One tip is to wrap the wire no more than 4 to 5 times around the spark plug, as close to the spark plug as possible. Second tip, even if you have a one cylinder, 4 stroke engine, you must set the tachometer to setting (1P1R) which is the setting for a 4 stroke 2 cylinder engine. But it works great.
Meter was packed in bubble wrap package and its white box was crushed, but no damage to meter. Meter is well built and includes battery. Delivered to Canada 1 month after order. Thanks.