If that is ok get one of the Isky Ratio Computers which is a small cardboard wheel that has a spinner on each side. One side will tell you about your tach readings, speedometer reading, speeds at what RPM & etc. The other side will give you all of the displacement figures. I have used them for years and they are very accurate. To determine if the tach is correct for example you would measure the diameter of your rear tires with them inflated and then use your rear end gear ratio and the speed your speedometer shows. Then when you move the part that turns to line these up it will show what the tach should read. They work for all of these things. I used to carry one in my car when I had it.
Ron
