Speedometers are present on everything drivable, from mopeds to big rigs. To protect the mechanism of the device, speedometers have a plastic covering. When cleaning a speedometer's face, you should exercise care in the tools and cleaners you use. Anything abrasive or containing strong solvents can result in scratching, clouding or discolouration of the plastic. This can create a barrier to viewing the speedometer.
Wipe away any dust present on the plastic surface with a microfiber cloth.
Apply 1/4 tsp of plastic polish to a foam wax applicator, and apply to the speedometer face using up-and-down and side-to-side motions.
Wipe the face with a clean microfiber cloth to remove all the plastic polish residue.
Spray the speedometer face with a layer of plastic spray-on sealant. Allow it to sit for 10 to 15 seconds. Wipe off with a clean microfiber cloth.
Test the quality of a microfiber cloth by rubbing it on the back of a blank CD. If the cloth scratches the CD, it will likely scratch your speedometer's plastic face. As an alternative to commercial products, you can make a soapy water solution with 1 cup of water and 5 or 6 drops of mild liquid dish soap. Dip a clean microfiber cloth into the soapy solution, and wipe the speedometer face. Wipe the face with a damp microfiber cloth to remove soap residue. Dry with a clean microfiber cloth.
If you own a motorcycle, never use a pressure washer on the speedometer face. Do not use strong solvents to clean the speedometer face, or damage could occur.