Hour meter
A meter that counts the hours the engine has run. On a truck that idles for hours at a dock, a piece of equipment that never moves far, or a boat with no odometer, running time is the wear figure, so maintenance is scheduled by hours instead of, or as well as, distance.
An odometer measures distance; an hour meter measures running time. For a car the two track each other closely enough that distance is the only reading a shop takes. For a working vehicle they come apart: a refuse truck or a delivery tractor can spend half its day running at a standstill, equipment is measured in hours by its maker, and a boat has no odometer at all. A twin-engine boat has two hour meters and no odometer, so a service record keyed to one meter per vehicle cannot describe it.
The consequence for the record is that a vehicle type decides its meters. A heavy truck carries an odometer and an hour meter; a powersport vehicle an hour meter; a boat one hour meter per engine; a trailer none. Each reading is taken at each visit, and each maintenance item in the preventive maintenance schedule is keyed to one of them.
In Wrenchy the vehicle type sets which meters a vehicle has, each reading is kept with the order it was taken on, and intervals are kept in the unit they belong to. The diesel and heavy-duty page is the page for the shops this matters to most.