Throwing grass into the wind can be helpful also.
I use a Perform aire eclipse that is very easy to use and seems to be accurate. I have had it for two years. I previously used a wet dry bulb, altimeter and temp meter to calculate the density altitude and one day woke up and decided to remove that time consuming job from my program and bought the eclipse. The dam thing gave nearly the same answer that the wet dry calculations gave me in one min. With my racer discount at jegs I paid $499.00, the asking price is $599.00
Bruce