Excelent

=IF(B9<>"",IF(B8="",E7+1,E8+1),IF(AND(B7<>"",B8="",B9<>""),E7+1,""))

^ ^
The Excel formula (in cell E9) necessary to allow my Fall Fitness Challenge log sheet to continue adding up the days I have worked out even if I enter in a date which I missed. I don't know why, but I love Excel. I voluntarily did a manual least squares data fit this afternoon 'cause it seemed nice. It differed from my visual estimate by only 0.067, or 0.2%. That was all after I wailed and moaned until I saw that my linearization of the solution to the linear ordinary differential equation resultant from Newton's Law of Cooling was incorrect in its logarithm algebra. What a happy moment when the theoretical temperature-vs-time plot lined up with the actual data!

I guess the point of this is to document in what manner and degree I enjoy Excel at the moment, and how much my mind is used to thinking about math, algebra, mathematics, and the use of math to describe physical phenomena. It's like pulling teeth, but I'm starting to get my mind back into schoolwork. Rrrg.

--An Ambassador With A High Refractive Index

[For those who care (i.e. Mike), column E is the total days worked out and column B is where I enter the time, if I worked out.]