Rate Of Change - ROC

See: Delta. And think: New minus Old, all over Old.

Think: your piggy bank. You reached down into its naughty places and, well, had to violate it to get your money out. At New Year's Eve last year, it had $28.36 in it. It's now a year later, and you do the same annual violation. You count $37.55. What's its delta, or rate of growth?

New: $37.55. So you subtract $28.36 from $37.55 and get $9.19. The old is $28.36...and you get about 32.4%. That's the rate of growth, year over year.

And yes, you can have a negative number as well: rate of shrinkage. Either way, they're rates of change.