The Treysit sirometer is a device that measures the speed of a gasoline-powered or electric motor in revolutions per minute, as well as its frequency in cycles. It features a sturdy Bakelite plastic cap that holds two simple analog meters, one for RPM and one for frequency. You can use this device to check the efficiency of riding or push lawn mower motors, power tool motors, boating motors and even motorcycle engines by pressing it firmly against the exterior case or housing of a running motor.
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Place the sirometer firmly against the case of any running motor.
Turn the inner dial of the sirometer to the left with one hand while maintaining pressure on the device with your other hand until an inch of wire protrudes from the indented slot that is located to the left of the dial.
Watch to see when the protruding wire vibrates cleanly and evenly, in resonance with the motor.
Read the top gauge and note the RPM reading. Read the bottom gauge and note the frequency reading.