I have a system which generates alerts for part usage but I worry its spamming them.

Part lifespan = 30,000 (approx 1 month),

Device A Average is 1% part lifespan per month or 300 counts per month
Device B Average is 100% so 30K per month

So how do I math? To get a dynamic usage figure. So say after 2 months time, Device B will say 100% twice, but Device A will say 20% by comparison.

countDiff = CountNow - HistoricCount
timeDiff = Now - HistoricDate

CountDiff/PartLifespan = Proxy1

Proxy1 / timeDiff (in months) = Dynamic % I need?

CountDiff/Average (per month) = Proxy2

Proxy2 / timeDiff (in months) = Dynamic % I need?

Is it the first option? If so what is the second one generating lol.