When you are blending, how do you measure?  Do you use a hydrometer?

Thanks,

Joe

No hydrometer, nothing that technical.  My tanks are 10 gallons so I break it down to 3 gallons  VP to 7 gallons 91.  I know that's not exactly 30%, but it's close enough for me.  If I'm mixing less than 10 gallons then I just do some quick math and and try to measure my blend. 
 
I'm planning on adding methanol injection so I can quit mixing and just run pump gas.  That seems to be a legit answer to "Do I have enough octane?".