A way to measure tapers for accuracy using 1-2-3 Blocks
With the blocks laying like this measure the diameter of the taper. Be careful to keep the jaws flat on the blocks to get an accurate measurement. This set up was quick and dirty just to show "how to".
Now with the blocks standing like this measure the diameter again. You are measuring exactly one inch away from your previous measurement. You will have looked up the taper per inch in your Machinery's Handbook and by subtraction you can find what taper per inch you have on your part. If it matches what the handbook calls for you are set. If not make an adjustment on your taper attachment or tail stock depending on what method you are using and tak another trial cut. Check frequently until you have the taper dead on.