[NoAction]

Sorry, I just now realized that my last sentence was very misleading. I was trying to simplify, but ended up sounding foolish. It is a bit more that just a simple ratio. I don't know how detailed you want to get, but the actual equation solved for time is: t=(halflife/.693)*ln(now/original).

[T. P. Pole]

I don't know how detailed you want to get, but the actual equation solved for time is: t=(halflife/.693)*ln(now/original). That, indeed, was more detail than I was after. Actually, I followed the last sentence about the ratios fine.