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I think you'd have to update the rank of all the other items at the same time that item gets zapped, otherwise item 's rank relative to other items might actually go down, because its old rank gets down-weighted via the exponent.
(As an example, imagine item gets a zap of just 1 sat. Its old rank gets down-weighted for time, by the increase from the 1 sat is negligible.)
Yes that's right. I store the sum because it's like the mantissa and the time because it's like the exponent. When a new zap comes in, the time allows me to discount the old sum.
I think that's right.