A customer asked us last month why their skid-steer’s CMH on our dashboard read 1,840 hours and the on-board hour meter read 2,210. Same machine, same week. 370 hours of difference.
Neither number was wrong. They were measuring different things and calling both of them “machine hours.”
This post is about that, because it’s the single most common source of confusion we see, and the definition you pick determines whether your maintenance program works.
The five definitions, ranked by what they try to capture
- Ignition on. The key is in the run position. Lights work. Radio works. Engine may or may not be running. This is what most factory hour meters measure on lighter equipment because it’s the cheapest thing to wire.
- Engine running. RPM is above an idle threshold. The machine is on, fuel is being burned, but the operator may be on a break with the engine idling.
- Engine running under load. RPM is above idle and hydraulic pressure or drive-train torque indicates the machine is doing work. Idle time doesn’t count.
- PTO engaged or hydraulics moving. A more specific version of #3 — the machine is running and a particular subsystem is active. Useful for attachments and implements.
- Operator present and inputs detected. Seat sensor + control input. The narrowest definition; closest to “the operator is using this thing.”
A piece of equipment that’s “on” 10 hours a day will rack up roughly:
- 10 hours under definition #1
- 9 hours under definition #2
- 6 hours under definition #3
- 4 hours under definition #4
- 3.5 hours under definition #5
Pick a different definition, get a different number. None of them are lies.
The number that wins
We default to definition #2, engine running, with #3 (engine under load) tracked alongside it as a secondary metric.
The reason: manufacturer service intervals are written in terms of engine hours, not work hours. The 500-hour oil change is 500 hours of the engine being on. If you track hours-under-load instead, you’ll under-service the equipment, because idle hours still wear the engine.
But hours-under-load is the better number for utilization questions — was this machine earning its keep, or sitting idle on a job site burning fuel. We track both and label them clearly. Calling either one “CMH” without saying which is how you get the 370-hour discrepancy.
Why this matters for the service interval
A skid-steer with a 500-hour oil change interval, tracked as ignition-on (definition #1) instead of engine-running (#2), gets serviced about 50 hours late. Once a year. Across a 50-machine fleet, that’s enough oil-related warranty arguments to pay for the telemetry twice over.
We’ve watched a customer move from clipboard CMH (a lossy approximation of #1) to telemetry CMH (clean #2) and discover their entire fleet had been over-serviced by 15%. They saved more on un-needed oil changes in the first quarter than the system cost for the year.
What we do in Fleet
Every asset has a primary CMH definition stored on the asset record, defaulting to “engine running” if the equipment supports an RPM signal and “ignition on” if it doesn’t. The dashboard surfaces both numbers when both are available, and the service-interval logic uses the one the manufacturer specified for that interval.
If you want hours-under-load instead, you can switch — but you’ll be arguing with the manufacturer’s warranty terms, and we’ll warn you about it before you do.
The takeaway
“Machine hours” is not a standard. It’s a category of measurement with five reasonable definitions and one wrong answer: not knowing which one you’re using.
Pick the definition that matches your service intervals. Label it explicitly. Make sure every report says which one it’s reporting. The rest of the maintenance program is built on top of that decision.