Either wipe your dipstick with or drip some oil on the wipe, and then wait a few seconds for the results. If the area saturated with oil quickly turns pink, then the oil still has life and does not need to be changed.
In 1999 Joe Gibbs racing got into making their own engine racing oil and oil products. How they found that economical with all the hundreds of other companies that are making the same stuff? No idea. http://www.drivenracingoil.com/
But this little innovation seems useful and unique, so I figured I'd give it a try.
Then I found out that due to supply of the specific material they needed for this, has stopped being produced. No, I don't know what that is, specifically. I called up this company and talked to Jonathan, and he was real nice, but he didn't know the specific material.
It's even sold out on Ebay. They won't be making any more.... so, what's that about? All the R and D to get a product out, market it, and everything, and then find out that since you're middle man between supply and demand, you're not going to have more to sell.
Well, sucks to not actually make anything yourself, but instead sell other peoples products as your own. Then find out your supplier ran out.