Actual Example:
The first owners of my rig purchased it for something less than its MSRP with owner modifications of $290,000.
7 years later, they traded the rig to a dealer for a newer rig.
The rig was then sold by the dealer for $120,000, with some sort of profit.
So, at almost precisely the 7 year old anniversary, the rig depreciated from MSRP, not including sales tax if any, $170,000 (or more if the dealer made a profit on resale).
Result:
69% depreciation in 7 years (10% straight line average) from MSRP.
$24,300 average annual loss in value each year.