How does Infinite Device Management calculate actual costs where there is a device purchase price and amortization period?

Suppose a device has a purchase price of 1200.00, and is amortized over 12 months. That works out to $100 / month for the first 12 months a device exists, and $0 / month afterwards.
 
Now, imagine that a device's purchase date is January 1, 2007. How would we calculate the actual cost for the device for the week of February 2 to February 9, 2007?
 
First, we determine that February 2 to February 9 represents 0.25 months exactly. In most cases, 1 week does not equal 0.25 months, but this particular week it does, so it's easier to explain.
 
Now, we realize that for all 0.25 of those months, the purchase price applies (there are no days after the end of the amortization period).
 
So, we have 1200 / 12 months = 100 / month * 0.25 months = $25 for that week. If we're doing cost per page, we then divide this $25.00 among all of the pages printed during that week to come up with the cost per page.
 
In summary, the following things matter:

  1. The purchase price
  2. The purchase date
  3. The amortization period
  4. The number of months we're looking at reporting on, (0.25 months in the above example).
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