By removing a spark plug and screw the adapter in its place, the Whistler Compression Ratio Meter, No. KAT-A0250, from Katech determines the compression ratio of virtually any engine to within a tenth of a point. A low-volume air source and 120V AC supply are required to use the Whistler. The device works with four-, six- and eight-cylinder engines ranging from six cu. in. to 600 cu. in. with a temperature range of 30 degrees F to 200 degrees F.