Parts and service revenue from a customer's installed units over what those units would generate at the rate the OEM's fully-contracted customers pay per unit per year, by model and age band.
Year-one units are under warranty; years three to eight generate the most. A young fleet has a low expected figure and is not a gap.
Units in the register against units shipped, per model and year. Where the register is short, expected is understated and the report says by how much.
Parts and service revenue from a customer divided by its installed units, compared with the norm for units of the same type and age band among customers who buy fully.
A customer runs 40 machines and buys $24,000 of parts a year: $600 per machine. Similar fleets buy $2,400. The gap is $72,000 a year at parts margins.
The installed base register is out of date, so the denominator is wrong. Units sold through distributors, resold or scrapped make attach look better or worse than it is.