A piece of paper, a pencil, and a wrist watch work wonders. I've used them every time I get a new engine. You don't need to be exact, just as long as you get the 10 hours before adding straight fuel. What's left in the tank will mix with the straight and give you some added protection for a few more hours.

Did that make any sense?

Mike is indeed correct on the little computers (he knows his hammers pretty well).